## 2 Optical and Electrochemical Sensing for Eukaryotic Cells and Bacteria
The integrated use of membrane-based sensors or combinations of micro dialysis is evoked to reinforce the ongoing research in the design of advanced nanomaterials-based in vivo electrochemical sensors, which may present exciting new avenues in neuroscience, since the understanding of the brain and of central and peripheral nervous system would provide unprecedented insights into the neurochemical basis of behavior and disease. [PERSON] and coworkers in their article: _Electrochemical Impedance Characterization of Cell Growth on Reduced Graphene Oxide-Gold Nanoparticles Electrodeposited on Indium Tin Oxide Electrodes_[7], describe the fabrication of reduced graphene oxide-gold nanoparticles (rGO-AuNP) electrodeposited onto a transparent indium tin oxide (ITO) electrode and investigate the feasibility of monitoring HEK293 cell growth by electrochemical impedance, in combination with the microscopic observation of the cells transfected with a green fluorescent protein expression vector. Results demonstrate the high potentiality of the rGO-AuNP/ITO electrode for label-free and real-time impedimetric cell-based assays, since the rGO-AuNP hybrids are biocompatible and induce an increase in cell adherence to the electrode when compared to the bare, AuNP-, or rGO-deposited ITO electrode. [PERSON] and coworkers in their paper on the _Development of an Electrochemical Biosensor for Rapid and Effective Detection of Pathogenic Escherichia coli in Licorice Extract_[8], describe the development of an aptamer-based electrochemical biosensor and its application in the rapid detection of pathogenic _Escherichia coli_ (_E. coli_) in licorice extract. For the biosensor fabrication, thiolated capture probes were firstly immobilized on a gold electrode, and then the biotinylated aptamer probes for _E. coli_ were introduced by hybridization with the capture probes. The sensing principle of the system is related to the stronger interaction between the aptamer and the _E. coli_, causing the dissociation of a part of the biotinylated aptamers from the capture probes in the presence of _E. coli_. Then, residual biotinylated aptamer probes can quantitatively bind with streptavidin-alkaline phosphatase and \(\alpha\)-naphthyl phosphate; substrates are catalytically hydrolyzed to generate an electrochemical response, recorded by a differential pulse voltammetry. This approach of electrochemical biosensing strategy can be used for developing other biosensors for pathogenic microorganisms and becomes a powerful tool for pathogenic bacteria's detection in the fields of food and drug safety, quality control, clinical diagnostics, and environmental monitoring. In the manuscript: _A Review on Nanoparticles as Boon for Biogas Producers--Nano Fuels and Biosensing Monitoring_[9], [PERSON] and coworkers overview the use of nanoparticles as an additive to feed bacteria that break down natural substances in bioenergy production from the biomass. The assessment of anaerobic digestion is based on the continuous monitoring of organic and volatile fatty acids, resulting in the accumulation of intermediates for unsteady progression conditions. Since instantaneous intervention is not possible due to the time between sampling and the availability of the results, acid content is typically only analyzed once or twice per month. To face this problem, biosensors have been devised for the accurate and fast analysis of many compounds. The focus of this manuscript is on the novel notion of dosing ions using modified nanoparticles that can be used to progress up biogas production in oxygen free digestion processes.