This paper reviews the potential of graphene as a material for fabricating various types of sensors. Graphene is a monolayer of carbon atoms which exhibits some remarkable electronic and mechanical properties and many of these properties lend themselves to sensor applications. The review attempts to be comprehensive in sensor types covering chemical and electrochemical sensors, magnetic and electric field sensors, optical sensors together with mass and strain sensors. The fact that graphene offers some advantages over this entire range of sensing modalities is an indication of its versatility and importance.
Magnetoresistive sensors using spin valves and magnetic tunnel junctions are reviewed, considering applications as readers in hard disk drives, as well as applications where the ultimate field detection limits are required ( from nT down to pT). The sensor noise level in quasi-DC or high-frequency applications is described, leading to sensor design considerations concerning biomedical and read head applications. Magnetic tunnel junction based sensors using MgO barriers appear as the best candidates for ultra-low field ( pT) detection, either in the high-frequency regime, or for quasi-DC applications.
Tuberculosis is one of the oldest known infectious diseases, responsible for millions of deaths annually around the world. The ability of Mycobacterium tuberculosis (Mtb) to enter into a dormant state has been considered integral to the success of this bacterium as a human pathogen. One of the key systems involved in regulating the entrance into dormancy is the differentially expressed in virulent strain sensor protein (DevS) [(dormancy survival sensor protein (DosS)]. However, the physiological signal for DevS has remained unclear since it was first shown to be a heme‐based sensor with conflicting reports on whether it is a redox or an oxygen sensor. To address this question and provide a better understanding of the electronic properties of this protein, we present here, for the first time, a series of spectroelectrochemistry measurements of the full‐length holo DevS in anaerobic conditions as well as bound to CO, NO, imidazole (Imz), cyanide, and O2. An interesting feature of this protein is its ability to bind Imz even in the ferrous state, implying small‐molecule analogues could be designed as potential regulators. Nonetheless, a midpoint potential (Em) value of +10 mV [vs normal hydrogen electrode (NHE)] for DevS as measured under anaerobic conditions is much higher than the expected cytosolic potential for Mtb or even within stimulated macrophages (~ −270 mV vs NHE), indicating this sensor works in a reduced ferrous state. These data, along with the high oxygen affinity and very slow auto‐oxidation rate of DevS, provides evidence that it is not a redox sensor. Overall, this study validates the biological function of DevS as an oxygen sensor directly involved in the dormancy/latency of Mtb. Spectroelectrochemical studies of the heme‐based sensor DevS from Mycobacterium tuberculosis (Mtb), a dormancy regulator, showed, for unliganded protein, an Em value of +11 mV (vs normal hydrogen electrode). This Em is much higher than the expected cytosolic potential for Mtb or even within stimulated macrophages (~ −270 mV), further supporting DevS is an oxygen sensor. A series of heme ligands and the effect of pH on the potential were investigated and discussed.
This review highlights the importance of coupling molecular imprinting technology with methodology based on electrochemical techniques for the development of advanced sensing devices. In recent years, growing interest in molecularly imprinted polymers (MIPs) in the preparation of recognition elements has led researchers to design novel formats for improvement of MIP sensors. Among possible approaches proposed in the literature on this topic, we will focus on the electrosynthesis of MIPs and on less common hybrid technology (e.g. based on electrochemistry and classical MIPs, or nanotechnology). Starting from the early work reported in this field, an overview of the most innovative and successful examples will be reviewed.