The measurement of sulfide, especially hydrogen sulfide, has held the attention of the analytical community due to its unique physiological and pathophysiological roles in biological systems. Electrochemical detection offers a rapid, highly sensitive, affordable, simple, and real-time technique to measure hydrogen sulfide concentration, which has been a well-documented and reliable method. This review details up-to-date research on the electrochemical detection of hydrogen sulfide (ion selective electrodes, polarographic hydrogen sulfide sensors, etc.) in biological samples for potential therapeutic use.

Nitric oxide (NO) plays an important role in physiological processes and it has been confirmed some human diseases are related to its biological function. Electrochemical sensors provide an efficient way to explore the NO function in biological processes. This review details different kinds of electrochemical sensors used for NO concentration detection between 2008 and 2013 together with their application in biological samples. Four commonly used electrodes and different assisted analysis membranes used for contributions towards the development of the novel sensors were summarized. Electrochemical sensors employed to measure NO concentration in a single cell, cell culture, tissue homogenate, organ, in vivo, human being, as well as in plant were also detailed. The trends of developing novel NO sensors were outlooked in the last part.

Nitric oxide (NO) has been considered as an important bio-regulatory molecule in the physiological process. All the existing methods often employed for NO measurement are mainly indirect and not suitable for in vivo conditions. In this paper, we report a systematic study of electrocatalytic NO reduction by comparing the redox properties of NO at carbon microelectrodes functionalized by Fe, Mn and Co protoporphyrins. The mechanisms of electrocatalytic reduction of NO by different metalloporphyrins have been proposed and compared. In addition, by varying the metallic cores of the metalloporphyrins, NO exhibits voltammograms in which the cathodic peak current occur at different potential. A comparative study on the electrochemical behavior of each of these metalloporphyrin (as a result of varying the metallic core) has been performed and a possible mechanism for the observed behavior is proposed. The results confirmed the potential applicability of using metalloporphyrins modified electrodes for voltammetric NO detection.

The NO electrode and membrane inlet mass spectrometry (MIMS) have the advantage of being sensitive, direct, and real time detectors of NO in aqueous solution. They do not require reacting NO with labels or purging of NO with an inert gas. We show that the NO electrode and MIMS are comparable in sensitivity detecting NO concentrations to 0.5 nM in aqueous solution, and both give identical results in a biological measurement, the reactions of deoxyhemoglobin with nitrite.

Morpholino has drawn considerable attention as a result of its advantageous properties. In the past few decades, morpholino has demonstrated in applications as being the premier knockdown tool in developmental biology because of its cytosolic delivery in the embryos through micro-injection. Morpholino has outstanding affinity for nucleic acids and the destabilizing effect of mismatches in morpholinocontaining heterodimers is higher than in a DNA or RNA double strand. Therefore, morpholino-based nucleic acid biosensors have high sensitivity and specificity for nucleic acid detection. In this review, the characteristics of morpholino are briefly introduced, followed by highlights of nucleic acid biosensors based on morpholino, including fabrication, analytical characteristics and biological applications.

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