Q.1 Which of the following best describes the principle of an ELISA (Enzyme-Linked Immunosorbent Assay)?
Detection of electrical impedance changes in a biosensor membrane
Enzymatic amplification of a colorimetric signal upon antigen-antibody binding
Magnetic resonance imaging of antigen-antibody complexes
Electrical conductivity measurement of antibody-coated electrodes
Explanation - ELISA uses an enzyme conjugated to a secondary antibody that catalyzes a color change when a substrate is added. The intensity of the color correlates with the amount of antigen present.
Correct answer is: Enzymatic amplification of a colorimetric signal upon antigen-antibody binding
Q.2 What is the role of a reference electrode in an amperometric biosensor?
To provide a constant potential against which the working electrode potential is measured
To serve as the site where the biorecognition event occurs
To amplify the current signal generated by the sensor
To act as a temperature control element
Explanation - The reference electrode maintains a stable potential so that the working electrode’s potential can be controlled precisely, allowing accurate current measurement.
Correct answer is: To provide a constant potential against which the working electrode potential is measured
Q.3 Which transduction principle is used by most electrochemical immunosensors?
Capacitance change due to antigen binding
Impedance measurement of the electrode surface
Voltage change induced by magnetic nanoparticles
Light scattering from labeled antibodies
Explanation - Impedance or electrochemical impedance spectroscopy (EIS) measures changes in the interface impedance caused by antigen–antibody binding, making it a common transduction method in immunosensors.
Correct answer is: Impedance measurement of the electrode surface
Q.4 In a sandwich ELISA, what is the role of the detection antibody?
To capture the antigen from the sample
To provide a secondary enzyme label for signal amplification
To block nonspecific binding sites
To initiate the color development step
Explanation - The detection antibody binds to a different epitope on the antigen than the capture antibody, and it is usually conjugated with an enzyme that produces the measurable signal.
Correct answer is: To provide a secondary enzyme label for signal amplification
Q.5 Which of the following is a key advantage of using electrochemical immunosensors over conventional ELISA?
Higher sample volume requirement
Longer assay time
Lower cost per test
Need for highly skilled technicians
Explanation - Electrochemical immunosensors often require smaller sample volumes, can provide rapid readouts, and have lower reagent costs compared to traditional ELISA assays.
Correct answer is: Lower cost per test
Q.6 What is the main function of the blocking reagent in ELISA protocols?
To enhance the enzymatic reaction rate
To prevent nonspecific binding of antibodies to the plate
To increase the sensitivity of the detection antibody
To stabilize the antigens during incubation
Explanation - Blocking reagents, such as BSA or casein, occupy nonspecific binding sites on the microplate, reducing background signal and improving assay specificity.
Correct answer is: To prevent nonspecific binding of antibodies to the plate
Q.7 Which type of electrode material is commonly used for its high surface area in nanostructured immunosensors?
Aluminum foil
Carbon nanotube composites
Copper wire
Gold-plated steel
Explanation - Carbon nanotubes provide a high surface area and excellent electrical conductivity, enhancing the sensitivity of electrochemical immunosensors.
Correct answer is: Carbon nanotube composites
Q.8 In impedance-based immunosensors, what does a decrease in the charge transfer resistance (Rct) typically indicate?
Formation of a thick protein layer
Loss of electrode functionality
Successful antigen binding to the antibody layer
Degradation of the electrode surface
Explanation - When an antigen binds to an antibody layer, electron transfer can be facilitated, reducing the charge transfer resistance observed in EIS measurements.
Correct answer is: Successful antigen binding to the antibody layer
Q.9 Which signal amplification strategy involves the use of DNA tags in electrochemical immunoassays?
Enzyme-mediated signal amplification
Electrochemical DNA amplification (EDA)
Magnetic nanoparticle-based amplification
Surface plasmon resonance enhancement
Explanation - DNA tags conjugated to antibodies can be amplified electrochemically, leading to increased current signals proportional to the target antigen concentration.
Correct answer is: Electrochemical DNA amplification (EDA)
Q.10 What is the purpose of a competitive ELISA format?
To detect very large antigens
To measure antibodies in a sample
To quantify antigens with limited epitope availability
To allow multiplex detection of several antigens simultaneously
Explanation - In competitive ELISA, the sample antigen competes with a labeled antigen for binding to a limited number of antibody sites, making it suitable for small or single-epitope antigens.
Correct answer is: To quantify antigens with limited epitope availability
Q.11 Which of the following is a characteristic advantage of label-free immunosensors?
Requires fluorescent tags
Prolonged assay times
Reduces complexity and cost of the assay
Limited to only electrochemical detection
Explanation - Label-free sensors detect binding events directly without the need for secondary labeled molecules, simplifying the assay workflow and cutting costs.
Correct answer is: Reduces complexity and cost of the assay
Q.12 In an amperometric immunosensor, which of the following is a key determinant of the sensor’s limit of detection (LOD)?
The thickness of the blocking layer
The electrode surface roughness
The incubation temperature
The optical clarity of the sample
Explanation - Surface roughness increases the effective area for electron transfer, improving sensitivity and lowering the LOD of amperometric sensors.
Correct answer is: The electrode surface roughness
Q.13 What is a major challenge when integrating immunodiagnostic biosensors into point-of-care devices?
Achieving high-throughput sample processing
Maintaining antigen stability over extended storage
Ensuring low cost of optical components
Providing a universal data communication protocol
Explanation - Immune reagents can degrade over time; point-of-care devices must preserve antigen and antibody activity, often requiring refrigeration or lyophilization.
Correct answer is: Maintaining antigen stability over extended storage
Q.14 Which of the following materials is commonly used to immobilize antibodies on microelectrode surfaces due to its biocompatibility and conductivity?
Polystyrene
Polydimethylsiloxane (PDMS)
Polypyrrole
Glass
Explanation - Polypyrrole is a conductive polymer that can be deposited onto electrode surfaces, providing a favorable environment for antibody attachment while maintaining electrical conductivity.
Correct answer is: Polypyrrole
Q.15 How does a surface plasmon resonance (SPR) immunosensor detect antigen binding?
By measuring changes in electrical current
By detecting shifts in reflected light wavelength
By monitoring temperature changes
By analyzing fluorescence intensity
Explanation - SPR detects changes in the refractive index near a metal film surface when antigens bind, causing a measurable shift in the reflected light’s resonance wavelength.
Correct answer is: By detecting shifts in reflected light wavelength
Q.16 Which of the following is a typical sample matrix used in immunodiagnostic assays?
Silicone oil
Blood serum
Phosphorus trichloride
Hydrogen peroxide
Explanation - Blood serum is a common biological sample used for detecting pathogens, biomarkers, or drug levels via immunoassays.
Correct answer is: Blood serum
Q.17 In the context of immunodiagnostics, what does the term 'sensitivity' refer to?
The assay’s ability to avoid cross-reactivity
The lowest concentration of antigen that can be reliably detected
The speed at which the assay produces a result
The ability to detect multiple antigens simultaneously
Explanation - Sensitivity measures how small a concentration of analyte can be detected by the assay, often expressed as the limit of detection.
Correct answer is: The lowest concentration of antigen that can be reliably detected
Q.18 What is the purpose of a capture antibody in a sandwich immunoassay?
To block nonspecific sites on the surface
To bind the sample antigen and immobilize it on the substrate
To provide the enzymatic label
To wash away unbound material
Explanation - The capture antibody is immobilized on a solid support and selectively binds the target antigen, allowing subsequent detection with a labeled antibody.
Correct answer is: To bind the sample antigen and immobilize it on the substrate
Q.19 Which detection method in immunoassays typically requires a secondary labeled antibody?
Direct ELISA
Indirect ELISA
Tandem mass spectrometry
NMR spectroscopy
Explanation - Indirect ELISA uses a primary antibody specific to the antigen, followed by a labeled secondary antibody that binds to the primary, producing a detectable signal.
Correct answer is: Indirect ELISA
Q.20 In electrochemical impedance spectroscopy (EIS), what does a semicircular feature in the Nyquist plot generally indicate?
Capacitive behavior of the double layer
Charge transfer resistance at the electrode interface
Faradaic reaction at the electrode surface
Ohmic resistance of the solution
Explanation - A semicircle in the Nyquist plot corresponds to the time constant associated with charge transfer resistance, which changes upon antigen binding.
Correct answer is: Charge transfer resistance at the electrode interface
Q.21 What is a common method for increasing the surface area of a glassy carbon electrode for immunosensor applications?
Polishing with fine sandpaper
Coating with a thin gold film
Electrochemical oxidation to create nanostructures
Immersing in an acid bath for prolonged periods
Explanation - Electrochemical oxidation can generate nanostructured features on the electrode surface, increasing the available area for antibody attachment and improving sensitivity.
Correct answer is: Electrochemical oxidation to create nanostructures
Q.22 Which of the following is a key consideration when selecting a transducer for an immunodiagnostic device?
The color of the transducer material
The magnetic permeability of the sample
Compatibility with the biorecognition element
The brand name of the manufacturer
Explanation - The transducer must maintain the functional integrity of antibodies or antigens, which requires suitable surface chemistry and mechanical stability.
Correct answer is: Compatibility with the biorecognition element
Q.23 Which of the following is NOT typically considered a characteristic of a good immunosensor?
High selectivity
Rapid response time
Inexpensive raw materials
Low sample volume requirement
Explanation - While cost is important, the primary characteristics are selectivity, sensitivity, speed, and sample volume; raw material cost is secondary.
Correct answer is: Inexpensive raw materials
Q.24 What is the primary advantage of using nanomaterials in immunosensor design?
They simplify the manufacturing process
They increase the electrical resistance of the sensor
They provide a high surface area for antibody immobilization
They reduce the need for temperature control
Explanation - Nanomaterials such as gold nanoparticles or carbon nanotubes offer a large surface area, improving the density of immobilized antibodies and thus the sensor’s sensitivity.
Correct answer is: They provide a high surface area for antibody immobilization
Q.25 Which signal transduction technique directly measures the change in optical properties due to antigen–antibody interaction?
Electrochemical impedance spectroscopy
Colorimetric detection
Resonant frequency shift detection
Fluorescence resonance energy transfer (FRET)
Explanation - FRET detects energy transfer between two fluorophores when they are in close proximity, which occurs when a labeled antibody binds to an antigen, altering the optical signal.
Correct answer is: Fluorescence resonance energy transfer (FRET)
Q.26 Which of the following best describes a lateral flow immunoassay (LFIA)?
A technique that requires a microfluidic chip
A test strip that displays results via color change on a paper strip
An electrochemical assay performed in a microplate
A mass spectrometry-based detection method
Explanation - LFIA is a point-of-care format where a sample migrates through a paper strip; antigen–antibody complexes produce a visible line, indicating the presence of the target.
Correct answer is: A test strip that displays results via color change on a paper strip
Q.27 Which of the following is a common method for measuring the concentration of an analyte in an ELISA?
Absorbance measurement at 450 nm
Differential scanning calorimetry
Nuclear magnetic resonance spectroscopy
X-ray diffraction
Explanation - The colorimetric substrate in ELISA often yields a product that absorbs maximally at 450 nm; this absorbance is proportional to the analyte concentration.
Correct answer is: Absorbance measurement at 450 nm
Q.28 What is the main purpose of a washing step in an ELISA?
To sterilize the plate
To remove unbound antibodies and reduce background noise
To add the detection reagent
To fix the antigen to the plate
Explanation - Washing removes any reagents that have not specifically bound, thereby minimizing nonspecific signal and increasing the assay’s specificity.
Correct answer is: To remove unbound antibodies and reduce background noise
Q.29 Which of the following is a typical detection limit achievable by a modern electrochemical immunosensor?
10 mg/mL
10 µg/mL
10 ng/mL
10 pg/mL
Explanation - Advanced electrochemical immunosensors can detect very low concentrations, often in the picogram per milliliter (pg/mL) range, enabling early biomarker detection.
Correct answer is: 10 pg/mL
Q.30 Which of the following is an advantage of using a fluorescent label over an enzyme label in immunoassays?
It allows for signal amplification without substrates
It is cheaper to produce
It requires longer incubation times
It is less specific
Explanation - Fluorescent labels can be excited and produce a detectable signal directly, and they can be amplified through methods like fluorescence resonance energy transfer.
Correct answer is: It allows for signal amplification without substrates
Q.31 What does a 'signal-to-noise ratio' (SNR) indicate in the context of an immunosensor?
The ratio of specific antibody concentration to nonspecific antibody concentration
The ratio of the measured signal to background noise
The speed of signal generation
The number of detection events per second
Explanation - A higher SNR means that the sensor’s signal is easily distinguishable from the background, which is critical for accurate detection.
Correct answer is: The ratio of the measured signal to background noise
Q.32 Which of the following is a key component in a typical microfluidic immunoassay chip?
Microchamber with a large volume
Microchannels for reagent mixing
Large glass window for optical imaging
Heavy metal containment zone
Explanation - Microfluidic chips use small channels to direct and mix fluids with high precision, enabling rapid and low-volume immunoassays.
Correct answer is: Microchannels for reagent mixing
Q.33 In a competitive ELISA, what is the relationship between the concentration of antigen in the sample and the intensity of the signal?
Directly proportional
Inversely proportional
Independent
Exponentially proportional
Explanation - Higher antigen concentrations in the sample compete more effectively with the labeled antigen, reducing signal intensity.
Correct answer is: Inversely proportional
Q.34 What is the primary role of a secondary antibody conjugated to horseradish peroxidase (HRP) in ELISA?
To capture antigens from the sample
To amplify the colorimetric signal
To block nonspecific sites
To serve as a reference standard
Explanation - HRP catalyzes the oxidation of a substrate, producing a measurable color change, thereby amplifying the detection signal.
Correct answer is: To amplify the colorimetric signal
Q.35 Which technique is often used to characterize the morphology of nanostructured electrodes in immunosensor fabrication?
Transmission electron microscopy (TEM)
Fourier-transform infrared spectroscopy (FTIR)
Dynamic light scattering (DLS)
Thermogravimetric analysis (TGA)
Explanation - TEM provides high-resolution images of nanostructures, allowing assessment of size, shape, and distribution on electrode surfaces.
Correct answer is: Transmission electron microscopy (TEM)
Q.36 Which of the following is a typical detection limit for a commercial point-of-care lateral flow test?
1 mg/mL
1 µg/mL
1 ng/mL
1 pg/mL
Explanation - Most lateral flow tests detect concentrations in the nanogram per milliliter range; higher sensitivity requires more sophisticated readouts.
Correct answer is: 1 ng/mL
Q.37 Which of the following best describes the working principle of a piezoelectric immunosensor?
Changes in mass on the crystal surface alter its resonant frequency upon antigen binding
The sensor emits light when antigen binds
The sensor measures changes in electrical resistance due to antigen binding
The sensor changes its color upon antigen binding
Explanation - Piezoelectric crystals vibrate at a specific frequency; binding of biomolecules changes the mass and shifts the frequency, which is measured.
Correct answer is: Changes in mass on the crystal surface alter its resonant frequency upon antigen binding
Q.38 Which of the following is an advantage of using magnetic nanoparticles in immunoassays?
They increase the viscosity of the sample
They simplify the washing step by enabling magnetic separation
They provide a direct optical signal
They reduce the need for a reference electrode
Explanation - Magnetic nanoparticles can be separated from solution using a magnet, streamlining cleanup and reducing background interference.
Correct answer is: They simplify the washing step by enabling magnetic separation
Q.39 What is the primary purpose of a blocking buffer in ELISA?
To neutralize the pH
To prevent non-specific binding of proteins
To increase the speed of the enzymatic reaction
To stabilize the substrate
Explanation - Blocking agents occupy nonspecific sites on the plate surface, thereby reducing background signal and improving assay specificity.
Correct answer is: To prevent non-specific binding of proteins
Q.40 Which of the following parameters is NOT directly affected by the incubation temperature in an ELISA?
Binding kinetics of antibodies and antigens
Rate of enzymatic conversion of the substrate
Viscosity of the buffer solution
The color of the substrate solution
Explanation - Temperature influences reaction kinetics and binding rates but does not change the inherent color of the substrate until reaction occurs.
Correct answer is: The color of the substrate solution
Q.41 Which type of electrochemical detection involves measuring the current that results from the oxidation or reduction of a species at the electrode surface?
Potentiometry
Amperometry
Conductometry
Capacitance measurement
Explanation - Amperometry monitors the current produced at a fixed potential, making it suitable for detecting changes in concentration of electroactive species.
Correct answer is: Amperometry
Q.42 In a sandwich ELISA, what is the function of the detection antibody conjugated with horseradish peroxidase (HRP)?
To bind the capture antibody
To catalyze the colorimetric reaction for signal detection
To act as a blocking reagent
To wash away unbound antigen
Explanation - The detection antibody carries the HRP enzyme, which converts the substrate into a colored product, providing a measurable signal.
Correct answer is: To catalyze the colorimetric reaction for signal detection
Q.43 Which of the following is a common method for quantifying the amount of antibody immobilized on a sensor surface?
Mass spectrometry
Surface plasmon resonance (SPR)
Infrared spectroscopy
X-ray fluorescence (XRF)
Explanation - SPR can detect changes in the refractive index at the sensor surface, allowing quantification of protein layers such as immobilized antibodies.
Correct answer is: Surface plasmon resonance (SPR)
Q.44 Which of the following statements best describes a lateral flow immunoassay (LFIA) detection principle?
Fluorescence intensity measurement
Colorimetric change on a test strip
Electrochemical signal generation
Mass spectrometric detection
Explanation - LFIA typically uses gold nanoparticles or colored conjugates that produce visible lines indicating the presence of the target analyte.
Correct answer is: Colorimetric change on a test strip
Q.45 What is the main advantage of using a label-free detection method in immunoassays?
It requires expensive labeled reagents
It provides rapid results without additional labeling steps
It increases assay complexity
It necessitates large sample volumes
Explanation - Label-free methods directly detect the binding event, simplifying the assay and reducing time and cost.
Correct answer is: It provides rapid results without additional labeling steps
Q.46 Which of the following is a commonly used signal amplification strategy in electrochemical immunoassays?
Use of high-conductivity electrodes only
Employing nanostructured surfaces and nanoparticles
Eliminating the detection antibody
Increasing the volume of the sample
Explanation - Nanostructured surfaces increase surface area, allowing more antibodies to be immobilized and improving sensitivity.
Correct answer is: Employing nanostructured surfaces and nanoparticles
Q.47 Which type of immunosensor typically relies on measuring changes in the refractive index near a sensor surface?
Surface plasmon resonance (SPR) sensor
Electrochemical impedance spectroscopy (EIS) sensor
Fluorescence-based sensor
Mass spectrometry-based sensor
Explanation - SPR detects minute changes in the refractive index caused by antigen–antibody interactions on a metal-coated surface.
Correct answer is: Surface plasmon resonance (SPR) sensor
Q.48 Which of the following is a typical application of immunodiagnostics in medical diagnostics?
Determining the composition of soil
Measuring the blood glucose level in a diabetic patient
Testing the structural integrity of an aircraft wing
Assessing the viscosity of a chemical reactor feed
Explanation - Immunodiagnostics can detect biomarkers, including glucose, in bodily fluids for clinical monitoring and disease management.
Correct answer is: Measuring the blood glucose level in a diabetic patient
Q.49 In a typical sandwich ELISA, what is the sequence of reagent addition?
Detection antibody → Capture antibody → Sample
Capture antibody → Sample → Detection antibody
Sample → Capture antibody → Detection antibody
Detection antibody → Sample → Capture antibody
Explanation - The capture antibody is first immobilized, then the sample containing the antigen is added, followed by the detection antibody.
Correct answer is: Capture antibody → Sample → Detection antibody
Q.50 Which of the following is a primary limitation of using enzyme-based labels in immunoassays?
Enzymes are very stable under all conditions
Enzyme activity can be temperature sensitive
Enzymes generate no signal
Enzyme labels are inexpensive
Explanation - Enzymes require optimal temperature and pH for activity; deviations can reduce assay sensitivity.
Correct answer is: Enzyme activity can be temperature sensitive
Q.51 Which type of transducer is most suitable for a portable, battery-operated immunosensor?
Optical fiber-based sensor
Microfluidic chip with integrated electrodes
Large-scale spectrophotometer
High-precision mass spectrometer
Explanation - Microfluidic chips can be fabricated with low-power electronics and integrated electrodes, making them ideal for portable immunosensors.
Correct answer is: Microfluidic chip with integrated electrodes
Q.52 What is the primary advantage of using a gold surface for antibody immobilization?
It has a high melting point
It provides a clean, inert surface for self-assembled monolayers
It is non-conductive
It has magnetic properties
Explanation - Gold surfaces allow for the formation of self-assembled monolayers (SAMs), which enable controlled attachment of antibodies with preserved activity.
Correct answer is: It provides a clean, inert surface for self-assembled monolayers
Q.53 Which of the following is NOT a common source of interference in immunoassays?
Cross-reactivity with similar antigens
Presence of heterophile antibodies
Inaccurate pipetting
Properly calibrated detection system
Explanation - A properly calibrated system reduces interference; the other options can introduce erroneous results.
Correct answer is: Properly calibrated detection system
Q.54 Which of the following best describes a 'label' in the context of immunoassays?
The antibody that captures the antigen
A molecule attached to a detection antibody that generates a measurable signal
The sample container
The buffer solution used for washing
Explanation - Labels, such as enzymes, fluorophores, or nanoparticles, provide the detectable signal for quantifying the antigen–antibody interaction.
Correct answer is: A molecule attached to a detection antibody that generates a measurable signal
Q.55 Which of the following is a typical method for immobilizing antibodies onto a sensor surface?
Thermal deposition
Electrochemical grafting
Sputter coating
Vacuum sublimation
Explanation - Electrochemical grafting allows the formation of covalent bonds between the antibody and the electrode surface, improving stability.
Correct answer is: Electrochemical grafting
Q.56 What is the primary role of a detection antibody in a sandwich ELISA?
To capture the antigen from the sample
To bind a secondary antigen for signal amplification
To provide a colorimetric readout after binding
To block the binding sites on the plate
Explanation - The detection antibody binds to the antigen and is conjugated with an enzyme that generates a measurable color change.
Correct answer is: To provide a colorimetric readout after binding
Q.57 Which of the following is an example of a portable immunoassay device?
Centrifuge
Handheld glucose meter
Mass spectrometer
Microwave oven
Explanation - Handheld glucose meters are portable immunoassay devices that use antibody-based detection for glucose monitoring.
Correct answer is: Handheld glucose meter
Q.58 Which of the following best describes the principle of electrochemical impedance spectroscopy (EIS) in immunosensing?
Measurement of voltage across a circuit to detect antigen binding
Measurement of current at a fixed potential to quantify antigen concentration
Measurement of the changes in the interface resistance due to antigen binding
Measurement of temperature changes induced by antigen-antibody interactions
Explanation - EIS monitors changes in impedance, including resistance and capacitance, resulting from antigen binding events at the sensor surface.
Correct answer is: Measurement of the changes in the interface resistance due to antigen binding
Q.59 What is the purpose of using a 'secondary antibody' in ELISA?
To capture the antigen
To bind the primary antibody and carry a label for detection
To block non-specific sites on the plate
To act as the reference standard
Explanation - Secondary antibodies are conjugated with labels and bind to the primary antibody, allowing signal generation.
Correct answer is: To bind the primary antibody and carry a label for detection
Q.60 Which of the following is a key factor influencing the sensitivity of an electrochemical immunosensor?
The color of the detection antibody
The number of functional groups on the electrode surface
The viscosity of the buffer
The brand of the potentiostat
Explanation - Functional groups enable covalent attachment of antibodies, increasing the density of active sites and thereby sensitivity.
Correct answer is: The number of functional groups on the electrode surface
Q.61 Which of the following best describes the term 'limit of detection' (LOD) in immunosensing?
The maximum amount of antigen that can be measured
The lowest concentration of antigen that can be reliably distinguished from background noise
The time required to complete the assay
The number of antibodies on the sensor surface
Explanation - LOD indicates the smallest amount of analyte that can be detected with statistical significance.
Correct answer is: The lowest concentration of antigen that can be reliably distinguished from background noise
Q.62 Which type of immunodiagnostic technique uses magnetic separation to isolate antigen-antibody complexes?
Fluorescence microscopy
Magnetic immunoassay
Surface plasmon resonance
X-ray diffraction
Explanation - Magnetic immunoassays use magnetic beads coated with antibodies to capture antigens; a magnet separates the complexes for analysis.
Correct answer is: Magnetic immunoassay
Q.63 What is the main reason for performing a 'blocking' step after immobilizing the capture antibody on an ELISA plate?
To increase the assay speed
To reduce background signal caused by nonspecific binding
To activate the capture antibody
To calibrate the detection system
Explanation - Blocking saturates any remaining binding sites on the plate, preventing nonspecific adsorption of other proteins.
Correct answer is: To reduce background signal caused by nonspecific binding
Q.64 Which of the following is a typical detection limit for a well-optimized fluorescent immunoassay?
1 mg/mL
1 µg/mL
1 ng/mL
1 fg/mL
Explanation - Fluorescent immunoassays can reach extremely low detection limits, often in the femtogram per milliliter (fg/mL) range.
Correct answer is: 1 fg/mL
Q.65 In a competitive ELISA, which component is typically labeled with an enzyme?
The capture antibody
The sample antigen
The labeled antigen
The detection antibody
Explanation - In competitive ELISA, the antigen in the sample competes with a labeled antigen; the labeled antigen is usually conjugated to an enzyme.
Correct answer is: The labeled antigen
Q.66 Which of the following is a common method for visualizing the presence of an antigen in a lateral flow test strip?
Colorimetric change of a gold nanoparticle label
Fluorescence emission
Electrochemical current measurement
Mass spectrometric peaks
Explanation - Gold nanoparticles produce a visible color change (red or purple) when they accumulate on the test line.
Correct answer is: Colorimetric change of a gold nanoparticle label
Q.67 What is the purpose of adding a 'wash buffer' in an ELISA protocol?
To neutralize the reaction pH
To remove unbound antibodies and reduce background noise
To activate the enzyme conjugate
To fix the antigen onto the plate
Explanation - Wash buffers clear out unbound reagents, ensuring that only specific binding events contribute to the measured signal.
Correct answer is: To remove unbound antibodies and reduce background noise
Q.68 Which of the following is an example of an 'electrochemical' detection method in immunoassays?
Absorbance measurement at 450 nm
Fluorescence intensity reading
Impedance spectroscopy
Mass spectrometric analysis
Explanation - Impedance spectroscopy measures electrical impedance changes due to antigen–antibody binding and is commonly used in electrochemical immunoassays.
Correct answer is: Impedance spectroscopy
Q.69 What is a typical incubation temperature for antibody-antigen binding in most ELISA assays?
0°C
4°C
37°C
80°C
Explanation - Incubating at 37°C (body temperature) often maximizes the binding rate between antibodies and antigens.
Correct answer is: 37°C
Q.70 Which of the following is a key advantage of using a nanostructured electrode in an electrochemical immunosensor?
It reduces the need for a reference electrode
It provides a high surface area for antibody immobilization, improving sensitivity
It eliminates the need for a detection antibody
It increases the electrode’s mechanical strength
Explanation - Nanostructured surfaces allow more antibodies to attach, enhancing the sensor’s response to antigen binding.
Correct answer is: It provides a high surface area for antibody immobilization, improving sensitivity
Q.71 Which of the following is a typical output signal of a piezoelectric immunosensor?
Color change
Electrical current
Change in resonant frequency
Mass spectrometry peaks
Explanation - Piezoelectric crystals change their resonant frequency when mass is added to their surface due to antigen-antibody binding.
Correct answer is: Change in resonant frequency
Q.72 What does the term 'capture antibody' refer to in immunosensor design?
An antibody that is conjugated to an enzyme label
An antibody immobilized on a surface to bind the target antigen
An antibody used to wash the sensor surface
An antibody that blocks nonspecific binding sites
Explanation - Capture antibodies are fixed on the sensor surface to selectively bind the antigen from the sample.
Correct answer is: An antibody immobilized on a surface to bind the target antigen
Q.73 Which of the following is a typical application of an immunodiagnostic assay in environmental monitoring?
Detection of bacterial contamination in water
Measuring the pH of soil
Testing the tensile strength of plastic
Analyzing the viscosity of oil
Explanation - Immunodiagnostic assays can identify specific bacterial antigens or toxins in environmental samples.
Correct answer is: Detection of bacterial contamination in water
Q.74 Which of the following is a key benefit of using a microfluidic platform for immunoassays?
Increased sample volume requirement
Longer assay time
Reduced reagent consumption and faster assay kinetics
Higher temperature operation
Explanation - Microfluidic devices allow precise control of small fluid volumes, improving assay speed and reducing costs.
Correct answer is: Reduced reagent consumption and faster assay kinetics
Q.75 What is the main function of the substrate in an ELISA?
To provide a binding site for the capture antibody
To be converted by the enzyme into a measurable signal
To block nonspecific binding sites
To wash away unbound reagents
Explanation - The substrate is enzymatically transformed into a colorimetric or fluorescent product, allowing quantification.
Correct answer is: To be converted by the enzyme into a measurable signal
Q.76 Which of the following is NOT a type of immunoassay?
ELISA
Western blot
PCR
Immunochromatographic assay
Explanation - PCR amplifies DNA, not proteins or antigens, so it is not considered an immunoassay.
Correct answer is: PCR
Q.77 In an electrochemical immunosensor, what is the purpose of a 'signal amplification strategy' such as using nanomaterials?
To reduce the sensor’s sensitivity
To enhance the detection signal without increasing the target concentration
To increase the required sample volume
To complicate the sensor design
Explanation - Nanomaterials can provide additional catalytic sites or increase surface area, boosting the electrical signal.
Correct answer is: To enhance the detection signal without increasing the target concentration
Q.78 Which of the following is an advantage of a label-free immunosensor over a labeled one?
Requires more complex instrumentation
Longer assay times
Simpler workflow and lower cost
Higher reagent consumption
Explanation - Label-free sensors detect binding directly, eliminating the need for additional labeled reagents and steps.
Correct answer is: Simpler workflow and lower cost
Q.79 Which of the following is a typical readout in a fluorescence-based immunoassay?
Change in current
Emission of photons at a specific wavelength
Resonant frequency shift
Mass change on the sensor surface
Explanation - Fluorescence-based assays measure the intensity of emitted light after excitation.
Correct answer is: Emission of photons at a specific wavelength
Q.80 What is a key difference between a direct and indirect ELISA?
Direct ELISA uses a labeled primary antibody while indirect ELISA uses an unlabeled primary antibody
Direct ELISA uses a labeled secondary antibody while indirect ELISA uses a labeled primary antibody
Indirect ELISA requires no washing steps
Direct ELISA is used only for protein detection
Explanation - In direct ELISA the primary antibody is conjugated to a label, whereas in indirect ELISA the primary is unlabeled and a labeled secondary antibody is used.
Correct answer is: Direct ELISA uses a labeled primary antibody while indirect ELISA uses an unlabeled primary antibody
Q.81 Which of the following is a common application of immunodiagnostics in veterinary medicine?
Determining the age of an animal
Detecting viral antigens in animal serum
Measuring blood sugar levels in plants
Analyzing soil composition
Explanation - Immunodiagnostic tests can identify pathogens in animal blood, aiding in disease control.
Correct answer is: Detecting viral antigens in animal serum
Q.82 Which of the following best describes a 'sandwich' format in immunoassays?
A single antibody captures the antigen, and a second antibody provides detection
The antigen is captured by a primary antibody and then detected by a secondary antibody that binds a different epitope
The sample is sandwiched between two detection reagents
The detection reagent is placed beneath the capture antibody
Explanation - The sandwich format uses two antibodies binding distinct sites on the antigen, improving specificity.
Correct answer is: The antigen is captured by a primary antibody and then detected by a secondary antibody that binds a different epitope
Q.83 Which of the following is a typical method for measuring the binding kinetics of antibody–antigen interactions in an immunosensor?
Electrochemical impedance spectroscopy (EIS)
Thermal gravimetric analysis (TGA)
Differential scanning calorimetry (DSC)
X-ray crystallography
Explanation - EIS can monitor changes in impedance over time, providing kinetic data on the binding process.
Correct answer is: Electrochemical impedance spectroscopy (EIS)
Q.84 What is the primary benefit of using a gold nanoparticle (AuNP) label in a lateral flow test?
They increase the sample volume
They provide a strong, visible color change for detection
They require high-temperature conditions
They reduce the need for a capture antibody
Explanation - Gold nanoparticles scatter light strongly, producing a visible line on the test strip.
Correct answer is: They provide a strong, visible color change for detection
Q.85 Which of the following is an example of a 'signal' in a biosensor?
The target antigen itself
The sensor’s output (e.g., current, voltage, optical signal)
The reference electrode potential
The temperature of the sample
Explanation - A signal is the measurable quantity that is generated in response to the analyte binding.
Correct answer is: The sensor’s output (e.g., current, voltage, optical signal)
Q.86 In a typical ELISA, what is the role of the 'substrate buffer'?
To provide optimal pH and ionic strength for the enzyme’s activity
To block nonspecific binding
To immobilize antibodies
To wash away unbound reagents
Explanation - The substrate buffer ensures the enzyme remains active and the reaction proceeds efficiently.
Correct answer is: To provide optimal pH and ionic strength for the enzyme’s activity
Q.87 Which of the following best describes the term 'analytical sensitivity' in immunoassays?
The ability to detect low concentrations of an analyte
The time it takes to perform the assay
The level of background noise in the measurement
The specificity for a particular antigen
Explanation - Analytical sensitivity refers to the lowest analyte concentration that can be reliably measured.
Correct answer is: The ability to detect low concentrations of an analyte
Q.88 Which of the following is a major challenge when designing an immunosensor for a clinical laboratory?
Ensuring the sensor can detect high concentrations only
Maintaining antibody functionality after immobilization
Making the sensor larger in size
Increasing the required sample volume dramatically
Explanation - Immobilization can denature antibodies, compromising specificity and sensitivity.
Correct answer is: Maintaining antibody functionality after immobilization
Q.89 Which of the following is a key characteristic of a 'label-free' detection method in immunoassays?
It requires an enzyme conjugate
It can detect antigen binding directly without additional labeling
It always uses a fluorescent tag
It requires a complex instrumentation setup
Explanation - Label-free methods, such as SPR or EIS, measure changes in physical properties caused by binding events.
Correct answer is: It can detect antigen binding directly without additional labeling
Q.90 Which of the following best describes the 'limit of quantitation' (LOQ) in immunoassays?
The highest analyte concentration that can be measured
The lowest analyte concentration that can be measured with acceptable precision and accuracy
The time needed to complete the assay
The maximum number of samples processed per day
Explanation - LOQ is the lowest concentration where the assay provides reliable quantitative results.
Correct answer is: The lowest analyte concentration that can be measured with acceptable precision and accuracy
Q.91 Which of the following is a common method to prevent non-specific binding in an immunoassay?
Using a high-temperature incubation
Adding a blocking agent (e.g., BSA) during incubation
Using a very high concentration of the detection antibody
Skipping the wash steps entirely
Explanation - Blocking agents occupy nonspecific sites, reducing background signal.
Correct answer is: Adding a blocking agent (e.g., BSA) during incubation
Q.92 What is the main role of the 'secondary antibody' in an indirect ELISA?
To capture the antigen from the sample
To bind the primary antibody and provide a detectable label
To block nonspecific binding sites
To serve as a standard for calibration
Explanation - The secondary antibody is labeled and recognizes the primary antibody, enabling detection.
Correct answer is: To bind the primary antibody and provide a detectable label
Q.93 Which of the following is a typical detection limit for a well-optimized electrochemical immunosensor using nanomaterials?
10 mg/mL
10 µg/mL
10 ng/mL
10 pg/mL
Explanation - Nanomaterials enhance sensitivity, achieving detection limits in the picogram per milliliter range.
Correct answer is: 10 pg/mL
Q.94 Which of the following best describes a 'competitive' immunoassay format?
Antigens compete with labeled antigens for binding to a limited number of antibodies
Antibodies compete with labeled antibodies for binding to the antigen
Antigens compete with each other for detection
Detection antibodies compete with each other for binding to the antigen
Explanation - Competitive assays rely on competition between sample antigen and a labeled antigen for a fixed antibody amount.
Correct answer is: Antigens compete with labeled antigens for binding to a limited number of antibodies
Q.95 Which of the following is a common signal transduction technique used in a surface plasmon resonance (SPR) immunosensor?
Measuring changes in the electrical conductivity of the sensor surface
Monitoring shifts in resonance angle or wavelength due to refractive index changes
Recording changes in fluorescence intensity
Detecting variations in the sample’s mass
Explanation - SPR detects changes in refractive index at the sensor surface caused by binding events.
Correct answer is: Monitoring shifts in resonance angle or wavelength due to refractive index changes
Q.96 Which of the following is an advantage of using a magnetic bead-based immunoassay?
They increase the temperature requirement
They facilitate easy separation of target complexes via a magnet
They require large sample volumes
They reduce the need for a detection antibody
Explanation - Magnetic beads can be rapidly separated from solution, simplifying washing and reducing background noise.
Correct answer is: They facilitate easy separation of target complexes via a magnet
Q.97 Which of the following is NOT a typical component of a microfluidic immunoassay chip?
Microchannels
Valves
Large reservoirs for sample storage
Detection electrodes
Explanation - Microfluidic chips use small reservoirs; large reservoirs are incompatible with the micro-scale design.
Correct answer is: Large reservoirs for sample storage
Q.98 What is the role of a 'capture' antibody in a sandwich immunoassay?
To bind the detection antibody
To capture and immobilize the target antigen on the sensor surface
To amplify the signal
To act as a reference standard
Explanation - The capture antibody is immobilized on the sensor and selectively binds the target antigen from the sample.
Correct answer is: To capture and immobilize the target antigen on the sensor surface
Q.99 Which of the following is a typical detection method for an immunochromatographic test strip?
Colorimetric readout by gold nanoparticles
Fluorescence measurement
Electrical impedance change
Mass spectrometry
Explanation - Gold nanoparticles produce a visible color change on the test line, enabling visual readout.
Correct answer is: Colorimetric readout by gold nanoparticles
Q.100 In an ELISA, which component is responsible for the color development step?
Capture antibody
Detection antibody
Substrate
Wash buffer
Explanation - The substrate is converted by the enzyme conjugated to the detection antibody, resulting in a color change.
Correct answer is: Substrate
Q.101 Which of the following best describes a 'sandwich' ELISA?
Antibody–antigen interactions are detected by a direct label
A single antibody binds the antigen and produces a signal directly
Two antibodies bind the antigen at different epitopes, forming a 'sandwich' for signal detection
The antigen is sandwiched between two layers of enzyme
Explanation - The sandwich format uses a capture antibody and a detection antibody, providing high specificity.
Correct answer is: Two antibodies bind the antigen at different epitopes, forming a 'sandwich' for signal detection
Q.102 What is the main function of the reference electrode in an electrochemical immunosensor?
To provide a stable potential against which the working electrode is measured
To detect the antigen directly
To amplify the signal
To block nonspecific binding
Explanation - The reference electrode maintains a constant potential, allowing precise control of the working electrode potential.
Correct answer is: To provide a stable potential against which the working electrode is measured
Q.103 Which of the following is a key factor influencing the selectivity of an immunosensor?
The type of substrate used for the electrode
The specific antibody used for antigen capture
The volume of the sample
The ambient temperature during storage
Explanation - The antibody’s specificity determines the sensor’s selectivity toward the target antigen.
Correct answer is: The specific antibody used for antigen capture
Q.104 Which of the following is a common application of immunodiagnostics in food safety?
Measuring the pH of food
Detecting bacterial contamination or toxins in food products
Testing the texture of bread
Analyzing the color of fruit
Explanation - Immunoassays can rapidly identify specific foodborne pathogens or toxins in food samples.
Correct answer is: Detecting bacterial contamination or toxins in food products
Q.105 What is the purpose of the 'incubation step' in an ELISA?
To wash the plate
To allow the antibody–antigen binding reaction to occur
To add the substrate
To calibrate the detection system
Explanation - Incubation provides time for the specific interaction between antibodies and antigens to take place.
Correct answer is: To allow the antibody–antigen binding reaction to occur
Q.106 Which of the following best describes an electrochemical immunosensor’s output signal?
A color change visible to the naked eye
An electrical current or voltage change
A change in magnetic field
A shift in refractive index
Explanation - Electrochemical sensors generate electrical signals (current, voltage, impedance) upon antigen binding.
Correct answer is: An electrical current or voltage change
Q.107 Which of the following is NOT a typical component of a lateral flow test kit?
Sample pad
Conjugate pad with labeled antibodies
Detection and control lines on the nitrocellulose membrane
High-temperature incubator
Explanation - Lateral flow tests operate at ambient temperature and do not require high-temperature incubation.
Correct answer is: High-temperature incubator
Q.108 Which of the following is an example of a 'label-free' detection method in immunodiagnostics?
Fluorescence-based immunoassay
Surface plasmon resonance (SPR)
Enzyme-linked immunosorbent assay (ELISA)
Radioimmunoassay
Explanation - SPR directly measures changes in refractive index due to antigen–antibody binding without requiring labels.
Correct answer is: Surface plasmon resonance (SPR)
Q.109 Which of the following is a key advantage of using a microfluidic chip for immunoassays?
It requires large sample volumes
It increases the assay time
It allows rapid, low-volume, and automated testing
It necessitates complex instrumentation
Explanation - Microfluidic chips enable precise control over small fluid volumes, reducing reagent consumption and speeding up assays.
Correct answer is: It allows rapid, low-volume, and automated testing
Q.110 In a typical electrochemical immunosensor, what does the term 'working electrode' refer to?
The electrode that measures the potential difference
The electrode that serves as a reference for potential
The electrode that is functionalized with the capture antibody
The electrode used for washing
Explanation - The working electrode is the active sensing surface where antibody–antigen interaction occurs.
Correct answer is: The electrode that is functionalized with the capture antibody