Measurement of Neuropeptide Y in Aptamer-Modified Planar Electrodes

Electrochemical impedance spectroscopy (EIS) is a powerful technique for studying the interaction at electrode/solution interfaces. The adoption of EIS for obtaining analytical signals in biosensors based on aptamers is gaining popularity because of its advantageous characteristics for molecular recognition. Neuropeptide Y (NPY), the most abundant neuropeptide in the body, plays a crucial role with its stress-relieving properties. Quantitative measurement of NPY is imperative for understanding its role in these and other biological processes. Although aptamer-modified electrodes for NPY detection using EIS present a promising alternative, the correlation between the data obtained and the adsorption process on the electrodes is not fully understood. Various studies utilize the change in charge transfer resistance when employing an active redox label. In contrast, label-free measurement relies on changes in capacitance. To address these challenges, we focused on the interaction between aptamer-modified planar electrodes and their target, NPY. We proposed utilizing -ω*Zimag as the analytical signal, which facilitated the analysis of the adsorption process using an analogous Langmuir isotherm equation. This approach differs from implantable microelectrodes, which adhere to the Freundlich adsorption isotherm. Notably, our method obviates the need for a redox label and enables the detection of NPY at concentrations as low as 20 pg/mL. This methodology demonstrated exceptional selectivity, exhibiting a signal difference of over 20-to-1 against potential interfering molecules.

Electrochemical bio- and chemosensors for cancer biomarkers: Natural (with antibodies) versus biomimicking artificial (with aptamers and molecularly imprinted polymers) recognition

Electrochemical (EC) bio- and chemosensors are highly promising for on-chip and point-of-care testing (POST) devices. They can make a breakthrough in early cancer diagnosis. Most current EC sensors for cancer biomarkers' detection and determination use natural antibodies as recognition units. However, those quickly lose their biorecognition ability upon exposure to harsh environments, comprising extreme pH, humidity, temperature, etc. So-called "plastic antibodies," including aptamers and molecularly imprinted polymers (MIPs), are hypothesized to be a smart alternative to antibodies. They have attracted the interest of the sensor research community, offering a low cost-to-performance ratio with high stability, an essential advantage toward their commercialization. Herein, we critically review recent technological advances in devising and fabricating EC bio- and chemosensors for cancer biomarkers, classifying them according to the type of recognition unit used into three categories, i.e., antibody-, aptamer-, and MIP-based EC sensors for cancer biomarkers. Each sensor fabrication strategy has been discussed, from the devising concept to cancer sensing applications, including using different innovative nanomaterials and signal transduction strategies. Moreover, employing each recognition unit in the EC sensing of cancer biomarkers has been critically compared in detail to enlighten each recognition unit's advantages, effectiveness, and limitations.

Ag nanorod@PEI-Ag nanohybrid as an excellent signal label for sensitive and rapid detection of serum HER2

The accurate detection of Human epidermal growth factor receptor-2 (HER2) as a critical breast cancer biomarker can be essential for the early selection of therapeutic approaches. HER2 is a prominent component of a signaling network. Overexpression of the HER2 protein due to amplification of its gene leads to the development of an aggressive subtype of breast cancer. Patients with tumors that overexpress HER2 are eligible for treatment that significantly reduces mortality rates. Herein, we present a fast and simple method for detecting serum HER2. A new electrochemical label has been developed using charged Ag nanorod@ polyethylenimine-Ag (Ag NR@ PEI-Ag) nanohybrid. The synthesized Ag NR@PEI-Ag nanohybrid simultaneously has the electroactive property of silver and the large surface area of the PEI, which results in the enhancement of the detection signal. So, using Ag NR@PEI-Ag nanohybrid as the electrochemical label, a simple, fast, and sensitive electrochemical biosensor was designed to detect HER2. This way, after immobilizing HER2 aptamer on the Au electrode surface, HER2 or human serum was exposed to the aptamer. Then, the positively charged Ag NR@PEI-Ag nanohybrid was adsorbed onto the negatively charged aptamer-HER2 complex, and the current that was produced due to the Ag/AgCl reaction was measured as the electrochemical signal. The aptasensor shows a broad linear response from 10-12 to 10-7 g, a low detection limit (LOD) of 10 pg, and a total assay time of ~ 30 min.