Stainless steel electrochemical capacitive microneedle sensors for multiplexed simultaneous measurement of pH, nitrates, and phosphates
simultaneous electrochemical detection, faradaic capacitance, cyclic voltammetry, microneedle sensors, polyaniline, carbon nanotubes, cellulose nanocrystals, phosphate detection, pH detection, nitrate detection
Concerns for agri-food safety and environmental management require development of simple to use and cost- and time effective multiplex sensors for point-of-need (PON) chemical analytics by public end-user. Simultaneous detection of nitrates, phosphates, and pH is of importance in soil and water analysis, agriculture, and food quality assessment. This article demonstrates a suite of stainless steel microneedle electrochemical sensors for multiplexed measurement of pH, nitrate, and phosphate using faradaic capacitance derived from cyclic voltammetry as the mode of detection. The multi-target microneedle sensors were fabricated by layer-by-layer (LbL) assembly in a stainless steel hypodermic microneedle substrate. For nitrate sensing, the stainless steel was coated with carbon nanotube/cellulose nanocrystal (CNT)/CNC) decorated with silver nanoparticles (Ag). For pH measurement, the polyaniline (pANI) was coated onto the CNT/CNC@Ag film, while for phosphate detection, the CNT/CNC/Ag @pANI microneedle was further decorated with ammonium molybdenum tetrahydrate (AMT). The microelectrode platforms were characterized by FTIR, Raman, and microscopic techniques. The nitrate- and phosphate-based microneedle electrochemical sensors had excellent selectivity and sensitivity, with a determined limit of detection (LOD) of 0.008 mM and 0.007 mM, respectively. The pH microneedle sensor was responsive to pH in the linear range of 3–10. The three microneedle sensors yielded repeatable results, with a precision ranging from 4.0 to 7.5% RSD over the concentration ranges tested. The inexpensive (~ 1 $ CAD) microneedle sensors were successfully verified for use in quantification of nitrate, pH, and phosphate in brewed black coffee as a real sample. As such, the microneedle sensors are economical devices and show great promise as robust platforms for PON precision chemical analytics.
Mugo, S.M., Lu, W. & Lemieux, S. Stainless steel electrochemical capacitive microneedle sensors for multiplexed simultaneous measurement of pH, nitrates, and phosphates. Microchim Acta 189, 206 (2022). https://doi.org/10.1007/s00604-022-05307-4
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