Society’s lifestyle is changing. The internet of things (IoT) and artificial intelligence (AI) are gaining space in our daily life. In this context, wireless and biological sensors play an important role in the future development of IoT and AI devices. Electric sensors convert a given stimulus promoted in their environment into an electrical signal that is interpreted by a computer and translated into useful information for the end-users of IoT technologies. They are present in a diversity of environments around us with the principal purpose of making our life easier. Though it seems easy when the technology is in our hands, years of research are behind the final product. Biological sensors for medicine are one of the most challenging technologies to develop with enough robustness for reliable integration into smartphones and IoTs.
Figure 1. Illustration of how a biological sensor operates.
Biological sensors make use of biological molecules (e.g. antibody, enzyme, DNA probe, etc.) serving as receptors to detect certain target molecules (Figure 1). When an interaction occurs between the biological receptor and the target, the signal is electrically converted into legible and useful information (such as concentration of glucose in blood, positive-negative diagnostic for certain types of infectious disease, etc.). These types of sensors are promising for IoT technologies because they can be used in a point-of-care (PoC) diagnostic format. Since the first commercial PoC biological sensor was developed (glucose sensor by YSI in 1975 using Leland C. Clark’s technology), thousands of designs for diverse target molecules have been published. Nonetheless, few of them are commercially available because of technical challenges to make them robust. To achieve robustness, multidisciplinary teams have to work together to rigorously control and overcome important technical issues. In this paper, we include all the considerations and control points that must be taken into account to obtain functional electrochemical capacitive biological PoC sensors.
Our group, Nanobionics, in Sao Paulo, has been working in this field since 2012. Although it is a short period of time, we achieved an important development in the operation of these types of sensors around 2014-16; at the time, we referred to it simply as redox capacitive biosensors. In 2014 we started to develop the theory and to understand the meaning of an electrochemical capacitive signal. At that same time, we performed the first application of the strategy for the development of a PoC biosensor for the detection of C-reactive protein (CRP). Since then, dozens of papers about theory and applications for the detection of several targets have been published alone or with our collaborators in Oxford, UK.
After all those years of work in the field, we thought that it was the moment to push the field forward and to share our detailed protocol with the community with the main purpose of making the electrochemical capacitive biological PoC sensor broadly accessible. We thought (and we still think) that by doing this, other researchers will have the tools and the facilities to use electrochemical capacitance in their research and to make new discoveries. We are pleased to achieve this objective and we hope that our protocol gets the attention of both the biosensor and analytical chemistry communities.