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Herein, we describe an experimental approach for adapting the principles of Raman spectroelectrochemistry to electrodes controlled using a bipolar circuit. This method allows the simultaneous acquisition of spectroscopic data as a function of both the electrode potential and the chemical composition of a bimetallic alloy and can be generalized to other system variables. The electrochemical reduction of 4-nitrothiophenol (4-NTP) was carried out on bimetallic Ag/Au alloy gradients and monitored in situ using a confocal Raman microscope with 785 nm excitation. Continuous Ag/Au alloy gradients, in which the alloy composition varied from approximately 0.5 to 1.0 mole fraction Ag, were prepared by using bipolar electrodeposition and then modified with a monolayer of 4-NTP using self-assembly. 4-NTP monolayers on Au/Ag alloys were placed in a bipolar electrochemical cell and characterized as a function of applied potential and chemical composition by using surface-enhanced Raman scattering. The E 1/2 for NTP reduction was observed to be a strong function of the alloy composition, increasing by over 100 mV as the mole fraction of Ag varied from 0.5 to 1.0. In addition, spectroscopic evidence for the formation of the partially reduced intermediate, 4,4'-dimercaptoazobenzene (DMAB) at intermediate applied potentials, was also found. Bipolar Raman spectroelectrochemistry (BRSE) is a powerful tool for acquiring in situ multidimensional Raman spectroelectrochemical data.

Food safety is facing great challenges in preventing foodborne diseases caused by pathogenic pollution, especially in resource-limited areas. The rapid detection technique of microorganisms, such as immunological methods and molecular biological methods, plays a crucial key in timely bioanalysis and disease treatment strategies. However, it is difficult for these methods to simultaneously meet the criteria of simple operation, high specificity, and sensitivity, as well as low cost. Coconut water is known as the “water of life” in Hainan. It is a refreshing and nutritious beverage which is widely consumed due to its beneficial properties to health. Coconut water processing is an important pillar industry in Hainan. The detection of pathogenic microorganisms, such as Escherichia coli, in coconut water has become an important factor which has restricted the upgrading and development of this industry. Based on the needs of industrial development, we developed a microbial photoelectric detection system which was composed of a fluorescent probe detection reagent and a photoelectric sensor detection device. This system combined microbial enzyme targets, selective fluorescent substrate metabolism characteristics, and a photoelectric sensor signal transduction mechanism, which produce a strong signal with a high signal-to-noise ratio. The microbial detection system developed here has a simple structure, simple and convenient operation, short detecting time (≥2 h), and high sensitivity (1 CFU/mL). This system may also enable early warning and monitoring programs for other pathogenic microorganisms in order to promote the overall competitiveness of the Hainan coconut water industry.

The Cover Feature illustrates the use of confocal Raman microscopy in conjunction with bipolar electrochemistry to obtain multidimensional spectroelectrochemical data in situ. The bipolar cathode consists of a continuous composition gradient of electrodeposited Ag/Au modified with a 4‐nitrothiophenol (4‐NTP) self‐assembled monolayer (SAM). The alloy gradient is oriented 90° to the applied electric field, and SERS data collected at a series of points across the surface is used to map the redox state of the SAM as a function of electrode potential and alloy composition. Spectroelectrochemical measurements show that, when the alloy composition is mostly Au, 4‐NTP is directly reduced to 4‐aminothiophenol. In contrast, when the Ag content of the alloy increases, a two‐step mechanism becomes operative due to photochemical processes promoted by the changed optical characteristics of the Ag‐rich alloy. More information can be found in the Article by B. Wang et al.