Label-free impedance biosensors offer a promising approach for point-of-care and other applications due to their low cost, ease of miniaturization, and label-free operation. These sensors detect changes in surface impedance when target molecules bind to immobilized probes, enabling the identification of unlabeled DNA and protein targets. However, challenges such as selectivity, sensitivity, and reproducibility remain significant obstacles. Impedance biosensors measure electrical impedance in AC steady state, often using electrochemical impedance spectroscopy (EIS), which involves applying a small sinusoidal voltage and measuring the resulting current. This method allows for the detection of impedance changes without the need for special reagents, making it suitable for label-free operation. Affinity biosensors rely on the selective binding of targets to probes, with the affinity step determining the sensor's performance. The readout step involves detecting changes in surface properties, which can be influenced by factors such as probe density, target concentration, and environmental conditions. Selectivity is crucial in real-world applications where non-target molecules may interfere with detection. Techniques such as blocking agents and differential sensing are used to reduce nonspecific binding. The limit of detection is a key performance metric, influenced by the strength of probe-target interactions and the minimum detectable change in impedance. Detection limits are often determined in the absence of interfering molecules, but real-world samples may contain significant non-target components, affecting accuracy. Dynamic range, or the range of measurable concentrations, is also important for quantifying analytes. Amplification techniques, while useful in other biosensors, are not typically used in label-free impedance biosensors. Impedance measurement involves applying a voltage and measuring the resulting current, with the impedance calculated as the ratio of voltage to current. Electrodes, including working, reference, and counter electrodes, are essential for accurate measurements. Instrumentation such as potentiostats and EIS analyzers are used to measure impedance across a range of frequencies. Circuit models, including constant phase elements and double-layer capacitance, help interpret impedance data. Practical issues in label-free impedance biosensors include understanding the causes of impedance changes, which may arise from changes in dielectric properties, surface charge, or molecular conformation. These factors can influence the sensor's response curve, which relates sensor output to target concentration. The response curve is often logarithmic, indicating that the sensor output is proportional to the target concentration in the low-concentration regime. Challenges such as selectivity, sensitivity, and reproducibility must be addressed to improve the performance and commercialization of label-free impedance biosensors.Label-free impedance biosensors offer a promising approach for point-of-care and other applications due to their low cost, ease of miniaturization, and label-free operation. These sensors detect changes in surface impedance when target molecules bind to immobilized probes, enabling the identification of unlabeled DNA and protein targets. However, challenges such as selectivity, sensitivity, and reproducibility remain significant obstacles. Impedance biosensors measure electrical impedance in AC steady state, often using electrochemical impedance spectroscopy (EIS), which involves applying a small sinusoidal voltage and measuring the resulting current. This method allows for the detection of impedance changes without the need for special reagents, making it suitable for label-free operation. Affinity biosensors rely on the selective binding of targets to probes, with the affinity step determining the sensor's performance. The readout step involves detecting changes in surface properties, which can be influenced by factors such as probe density, target concentration, and environmental conditions. Selectivity is crucial in real-world applications where non-target molecules may interfere with detection. Techniques such as blocking agents and differential sensing are used to reduce nonspecific binding. The limit of detection is a key performance metric, influenced by the strength of probe-target interactions and the minimum detectable change in impedance. Detection limits are often determined in the absence of interfering molecules, but real-world samples may contain significant non-target components, affecting accuracy. Dynamic range, or the range of measurable concentrations, is also important for quantifying analytes. Amplification techniques, while useful in other biosensors, are not typically used in label-free impedance biosensors. Impedance measurement involves applying a voltage and measuring the resulting current, with the impedance calculated as the ratio of voltage to current. Electrodes, including working, reference, and counter electrodes, are essential for accurate measurements. Instrumentation such as potentiostats and EIS analyzers are used to measure impedance across a range of frequencies. Circuit models, including constant phase elements and double-layer capacitance, help interpret impedance data. Practical issues in label-free impedance biosensors include understanding the causes of impedance changes, which may arise from changes in dielectric properties, surface charge, or molecular conformation. These factors can influence the sensor's response curve, which relates sensor output to target concentration. The response curve is often logarithmic, indicating that the sensor output is proportional to the target concentration in the low-concentration regime. Challenges such as selectivity, sensitivity, and reproducibility must be addressed to improve the performance and commercialization of label-free impedance biosensors.