Lipid membranes regulate the flow of nutrients and communication signaling between cells and protect the sub-cellular structures. Recent attempts to fabricate artificial systems using nanostructures that mimic the physiological properties of natural lipid bilayer membranes (LBM) fused with transmembrane proteins have helped demonstrate the importance of temperature, pH, ionic strength, adsorption behavior, conformational reorientation and surface density in cellular membranes which all affect the incorporation of proteins on solid surfaces. Much of this work is performed on artificial templates made of polymer sponges or porous materials based on alumina, mica, and porous silicon (PSi) surfaces. For example, porous silicon materials have high biocompatibility, biodegradability, and photoluminescence, which allow them to be used both as a support structure for lipid bilayers or a template to measure the electrochemical functionality of living cells grown over the surface as in vivo. The variety of these media, coupled with the complex physiological conditions present in living systems, warrant a summary and prospectus detailing which artificial systems provide the most promise for different biological conditions. This study summarizes the use of electrochemical impedance spectroscopy (EIS) data on artificial biological membranes that are closely matched with previously published biological systems using both black lipid membrane and patch clamp techniques.

Prostate-specific antigen (PSA) is a commonly used biomarker for the detection of prostate cancer (PCa) and there are numerous data available for its invasive detection in the serum and whole blood. In this work, an electrochemical sensing method was devised to detect traces of PSA in human saliva using a hybrid nanocomposite of graphene nanoplatelets with diblock co-polymers and Au electrodes (GRP-PS₆₇-b-PAA₂₇-Au). The pure graphitic composition on filter paper provides significantly high electrical and thermal conductivity while PS₆₇-b-PAA₂₇ makes an amphiphilic bridge between GRP units. The sensor utilizes the binding of an anti-PSA antibody with an antigen-PSA to act as a resistor in a circuit providing an impedance change that in turn allows for the detection and quantification of PSA in saliva samples. A miniaturized electrical impedance analyzer was interfaced with a sensor chip and the data were recorded in real-time using a Bluetooth-enabled module. This fully integrated and optimized sensing device exhibited a wide PSA range of detection from 0.1 pg mL⁻¹ to 100 ng mL⁻¹ (R² = 0.963) with a lower limit of detection of 40 fg mL⁻¹. The performance of the biosensor chip was validated with an enzyme-linked immunosorbent assay technique with a regression coefficient as high as 0.940. The advantages of the newly developed saliva-PSA electrical biosensor over previously reported serum-PSA electrochemical biosensors include a faster response time (3–5 min) to achieve a stable electrical signal for PSA detection, high selectivity, improved sensitivity, no additional requirement of a redox electrolyte for electron exchange and excellent shelf life. The presented sensor is aimed for clinical commercialization to detect PSA in human saliva.

In this work, an ultra-sensitive electrochemical-digital sensor chip is devised for potential use as a digital stress analyzer for point-of-care testing (POCT) and preventive on-site recording of the hormone ‘cortisol’, a glucocorticoid class of steroid hormone present in the human saliva. The sensor was interfaced and re-configured with a high precision impedance converter system (AD5933) and used for electrochemical impedance spectroscopy (EIS) to evaluate the cortisol levels in seven saliva samples. To obtain enhanced biological (cortisol) recognition and achieve a lower limit of detection 0.87 ± 0.12 pg mL⁻¹ (2.4 ± 0.38 pmol mL⁻¹) with a wide range from 1 pg mL⁻¹ to 10 ng mL⁻¹ (2.75 pmol mL⁻¹ to 27.58 pmol mL⁻¹; R² = 0.9831), bovine serum albumin (1% BSA) was utilized as an effective sensitivity enhancer in addition to optimizing the other two parameters: (i) anti-cortisol antibody (anti-CAb) covalently attached to micro-Au electrodes and (ii) saliva sample incubation time on the sensor chip. The results obtained in this work were corroborated with the gold standard ELISA test with an accuracy of 96.3% and other previously reported biosensors. We envisage that the conceivable standpoint of this study can be a practice towards new development in cortisol biosensing, which will be pertinent to POCT targeted for in vitro psychobiological study on patient cortisol in saliva, and finally an implantable sensor chip in the future.