Know Your Sensor and Know Your Sample

Abstract

I am writing this piece to urge you to properly understand the sensing principle you are developing as well as the application you have in mind. Please know your sensor and your sample. In my role as Executive Editor of ACS Sensors, I see many submitted works where neither the sensing mechanism nor the analytical problem is properly understood or studied. Please spend time on the problem you aim to solve. This is a real opportunity, not an unnecessary burden, and should be seen as enriching. Chemistry is the science of change. Chemical and biochemical transformations occur in most samples of practical relevance and tracking them with sensors is an amazing opportunity to further our understanding of complex systems. Aquatic environments, for example, exhibit chemical gradients and temporal fluctuations driven by temperature, salinity, sunlight, bioactivity, exchange with the atmosphere, mixing, and interactions with colloidal and polymeric matter in addition to small molecules. Metal species may change their redox state, their chemical speciation through complexation, precipitation, adsorption, and bio-uptake. Organic pollutants are chemically transformed, taken up, adsorbed, and decomposed. In living systems, drugs are metabolized, ions fluctuate in space and time, chemical and biological species form gradients and compartmentalize, cells may rupture and change the sample environment, and the sensor itself can be attacked and fouled. Yes, these processes are challenging to understand but form an integral part of serious sensor research. But sensors and integrated assays should also be characterized and mechanistically understood in view of the analytical problem. Why is that? Some probes may be based on equilibrium interactions and tend to respond exclusively to a particular equilibrium species that interacts with the sensing species or surface. Other principles, as often encountered with dynamic electrochemistry, are mass-transport limited. Here, the reacting species can normally not be chemically isolated from other chemical forms that rapidly interconvert on the time scale of the experiment. This changes the chemical information the sensor will report on. A third class, as with many spectroscopic and separation principles, but also affinity assays and reaction-based molecular indicators, is based on a complete chemical or biological isolation or transformation. Here, information on chemical speciation tends to be all but lost unless special precautions are taken. So, do you know what information your sensor gives you? Is this information adequate for the system you aim to study? What reference method and what conditions should one choose to best correlate two different techniques? Please spend time on these important questions and do not just spike a target sample with the analyte of interest to call it a day. Yes, one should aim for adequate selectivity and sensitivity. But knowing what you measure and taking the complexities of your sample seriously will help your research to have real impact. And this should be our goal, not just to produce an academic paper. This article has not yet been cited by other publications.