In recent years, there has been an increased interest in the research and development of 2D materials for use and application in different fields, such as new technologies, medicine, health care, flexible biosensors, and wearable devices. Our goal is based on developing a flexible wearable biosensor for the skin to detect in real-time neurotransmitters and neuropeptides in human sweat. The development of flexible biosensors for detecting molecules in sweat has been of great interest. However, the problem is that most research has focused on a limited number of molecules such as lactate, chloride and potassium ions, glucose, and pH, and there is a great need to develop flexible biosensors that can monitor real-time molecules that are not yet studied in sweat. One of our molecules of great interest is neuropeptide Y (NPY). NPY has an essential role in the energy balance and is related to different diseases and conditions such as diabetes, obesity, depression, anxiety, and sleep problems and has recently been found to be associated with cardiovascular problems.

Our biosensor consists of flexible, low-cost materials that do not require much manufacturing time. The proposed flexible sensor system consists of paper-based microfluidics that serve as our system's passive flow method and silver inkjet electrodes printed on the PET surface. Microfluidic systems can be characterized as active or passive, depending on the force applied to the sample or flow. We can perform minimal flow or particles in a minimum amount of liquid or a sample flow with paper-based microfluidics systems. Among the passive microfluidic systems, paper-based microfluidics, also known as micro-pads, are among the most promising methods because they are easy to manufacture, inexpensive, and have low sample volume.

One of the most popular techniques to develop electrochemical wearable biosensors is the fabrication of microelectrode arrays through inkjet printing. To fabricate our electrode arrays, we first created the design in AutoCAD and then printed it using silver conductive ink and a commercial inkjet printer. Since sweat is a complex fluid, it is necessary to modify the working electrode's surface to give the electrode's selectivity towards the molecule to be analyzed or detected. To achieve the detection of NPY, we first add carboxyl groups to the surface of the working electrode, which will serve as an anchor for the specific aptamer for NPY. We use different buffer solutions like artificial cerebrospinal fluid, phosphate buffer solutions, and artificial sweat to perform electrochemical characterization on our silver inkjet electrodes through cyclic voltammetry and electrochemical impedance spectroscopy (EIS). We decreased the oxidation of the surface of our electrodes by changing the buffer and modifying the surface for greater selectivity towards NPY. Using 2D materials, we managed to manufacture and electrochemically characterize our flexible biosensor system prototypes to detect neuropeptides and neurotransmitters in sweat, applying the use of paper-based microfluidics and silver inkjet electrodes printed on PET and paper surfaces.