New multispecific array as a tool for electrochemical impedance spectroscopy-based biosensing.

Using electrochemical impedance spectroscopy (EIS) for biosensing applications typically requires repetitive experiments. To address this need, we have designed a multispecific electrochemical array with eight individually addressable 2mm-diameter gold working electrodes for rapid biosensing data accumulation by EIS in the presence of redox agent. The array allows to incorporate multiple negative controls in the course of a single binding experiment, as well as to perform parallel identical experiments to improve reliability of detection. The array is fit with attached electrochemical cell with Ag/AgCl mini reference electrode and can be used to process macro samples of 0.5-1 ml or micro samples of 5 microl in a drop-wise fashion. Eight individual EIS measurements are completed in 15 min. The reported array is disposable, economical and is easy to use. Examples of array use for label-free genetic sensing of 2.7 kb-long target Yersinia pestis DNA and for protein sensing of Ricin Toxin Chain A (RTA) are presented. We suggest the reported array design as a tool for researchers in the area of EIS sensing.

Challenges of electrochemical impedance spectroscopy in protein biosensing.

Electrochemical impedance spectroscopy (EIS) measurement, performed in the presence of a redox agent, is a convenient method to measure molecular interactions of electrochemically inactive compounds taking place on the electrode surface. High sensitivity of the method, being highly advantageous, can be also associated with nonspecific impedance changes that could be easily mistaken for specific interactions. Therefore, it is necessary to be aware of all possible causes and perform parallel control experiments to rule them out. We present the results obtained during the early stages of aptamer-based sensor development, utilizing a model system of human alpha thrombin interacting with a thiolated DNA aptamer, immobilized on gold electrodes. EIS measurements took place in the presence of iron ferrocyanides. In addition to known method limitations, that is, inability to discriminate between specific and nonspecific binding (both causing impedance increase), we have found other factors leading to nonspecific impedance changes, such as: (i) initial electrode contamination; (ii) repetitive measurements; (iii) additional cyclic voltammetry (CV) or differential pulse voltammetry (DPV) measurements; and (iv) additional incubations in the buffer between measurements, which have never been discussed before. We suggest ways to overcome the method limitations.

Biomaterial-based infrared detection.

This effort is focused on the use of crustacyanin protein extracted from the lobster shell in IR detection and imaging applications. In addition to the protein's excellent reversible thermo-active response in the IR region of interest, electrical characteristics versus temperature showed that the protein can be used as an electro-optic thermal sensing device as well. The high sensitivity and fast response of the protein layer were further enhanced by the deposition process we used. The thin coatings were prepared by Langmuir-Blodgett and self-assembly techniques. Furthermore, the protein exhibited temperature variation under Ti:sapphire laser excitation at different wavelengths in ambient environment. We have also shown that the protein exhibits fluorescence properties after exposure to IR heat. Stability of the protein, which is important in this type of application, was also demonstrated using the different characterization techniques after repeated heating/cooling cycles. We can conclude that this protein represents a formidable candidate for the fabrication of IR sensors and microbolometers for uncooled IR imaging applications.