Melanin as an active layer in biosensors

Abstract

The development of pH sensors is of great interest due to its extensive application in several areas such as industrial processes, biochemistry and particularly medical diagnostics. In this study, the pH sensing properties of an extended gate field effect transistor (EGFET) based on melanin thin films as active layer are investigated and the physical mechanisms related to the device operation are discussed. Thin films were produced from different melanin precursors on indium tin oxide (ITO) and gold substrates and were investigated by Atomic Force Microscopy and Electrochemical Impedance Spectroscopy. Experiments were performed in the pH range from 2 to 12. EGFETs with melanin deposited on ITO and on gold substrates showed sensitivities ranging from 31.3 mV/pH to 48.9 mV/pH, depending on the melanin precursor and the substrate used. The pH detection is associated with specific binding sites in its structure, hydroxyl groups and quinone imine.

Cephalopod‐Derived Biopolymers for Ionic and Protonic Transistors

“…The authors recorded the transistors' source–drain current as a function of the source–drain voltage (at constant gate voltages), as well as the source–drain current as a function of the reference electrode voltage (at constant source–drain voltages), as illustrated in Figure B . For both sets of current–voltage characteristics, the authors observed that the source–drain current increased as the pH of the buffer solution decreased, with a sensitivity that was comparable to the state‐of‐the‐art . The measurements showed that changes in the solution pH gated the electronic currents in eumelanin‐based EGFETs by altering the conductivity of the connected eumelanin films (presumably through protonation of surface functional groups and/or proton diffusion into the bulk).…”

“…This transistor architecture exposed the eumelanin films to the solution and made it possible to monitor the effect of changes in the environmental conditions on the films' electrical properties. The authors recorded the transistors' source–drain current as a function of the source–drain voltage (at constant gate voltages), as well as the source–drain current as a function of the reference electrode voltage (at constant source–drain voltages), as illustrated in Figure B . For both sets of current–voltage characteristics, the authors observed that the source–drain current increased as the pH of the buffer solution decreased, with a sensitivity that was comparable to the state‐of‐the‐art .…”

“…The conductivity of eumelanins was subsequently leveraged by Da Silva et al for applications in extended‐gate field effect transistors (EGFETs) . For this purpose, the authors fabricated devices consisting of a eumelanin film on a conductive substrate that was immersed in a buffer solution with a variable pH and connected to the gate of a standard metal oxide semiconductor field effect transistor (MOSFET), as illustrated in Figure A . This transistor architecture exposed the eumelanin films to the solution and made it possible to monitor the effect of changes in the environmental conditions on the films' electrical properties.…”

“…Copyright 2006, Springer. B) Reproduced under the terms of the Creative Commons CC BY License . Copyright 2014, The Authors, published by AIP Publishing.…”

An open-source equipment for thin film fabrication by electrodeposition, dip coating, and SILAR

“…In fact, the functioning of many electronic devices is based on semiconductor thin films. Some clear examples of commonly used devices based on thin films are transistors [1], OLEDs [2], biosensors [3,4], opto-electronic devices, and solar cells [5][6][7][8]. In the field of solar cells, the quality of the active semiconductor films is crucial for good functioning and energyharvesting performance [9,10].…”