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A paper-based analytical device (PAD) with an integrated composite electrode has been designed and fabricated for non-enzymatic creatinine sensing. Reduced graphene oxide (rGO) was employed to modify the PAD so that it could function as a solid-contact transducer. A new macrocyclic pyrido-hexapeptide derivative was made and used as a special ionophore in the creatinine membrane sensor. The synthesized PAD showed a detection limit of 1.0 µM (S/N = 3) and a potentiometric response towards creatinine throughout a log-linear range of 2.0 µM–10 mM (R2 = 0.9998). The sensor shows significant selectivity for a few related substances, including ephedrine, codeine, ketamine, caffeine, urea, urate, carbinoxamine, and dextromethorphan. It has been established that the testing method is appropriate for the direct potentiometric detection of creatinine in a variety of human urine sample types. When an indicating electrode and a reference electrode are put on the same flexible disposable, this lets applications with a small sample volume be done. For point-of-care creatinine measurement, the developed paper-based analytical equipment is a good choice because it is affordable, easily accessible, and self-pumping (especially when combined with potentiometric detection). [ABSTRACT FROM AUTHOR]

A paper-based analytical device (PAD) is presented with colorimetric/electrochemical dual readouts for the simultaneous sensing of total chromium (Cr) and hexavalent chromium (Cr(VI)). This device consists of a homemade three-electrode system and a patterned paper chip, integrating multiple functions including electrochemical detection, fluid driving, online oxidation, and colorimetric detection. The fiberglass filter paper with a hydrophilic microchannel was used to achieve self-driving fluidics without external equipment. One end of the microchannel was integrated with a homemade three-electrode system to achieve sample loading and electrochemical detection. The middle region on the microchannel was modified with oxidizing reagents to perform online pretreatment, and the yield of Cr(III) oxidation can reach 97.9%, ensuring reliable colorimetric detection of total Cr at another end of the microchannel modified with chromogenic agents. With this device, the signals of Cr(VI) (the signal peak at 0.29 V vs. Ag/AgCl) and total Cr can be obtained in one single injection. After optimization, the limit of detection (LOD) of Cr(VI) and total Cr were 0.01 mg L−1 and 0.06 mg L−1 and the linear ranges were 0.05–3.0 mg L−1 and 0.2–3.0 mg L−1, respectively. The relative standard deviations (RSD) of the electrochemical testing of Cr(VI) results were in a range 1.3%–8.7% (n = 3), and the RSD values of the colorimetric testing of total Cr were between 0.7–9.2% (n = 3). The device's reliability was demonstrated by performing the practical speciation of Cr in tap water, river water, and electroplating wastewater while the recoveries obtained using the present method were in the range 93.5–106%. Overall, the proposed device provides high application prospect in the on-site rapid Cr speciation. [ABSTRACT FROM AUTHOR]

A microcapillary grooved paper-based analytical device capable of dual-mode sensing (colorimetric and electrochemical detection) was demonstrated for analysis of viscous samples (e.g., human saliva). Herein, a hollow capillary channel was constructed via laser engraved micropatterning functions as a micropump to facilitate viscous fluidic transport, which would otherwise impede analysis on paper devices. Using salivary thiocyanate as a model analyte, the proposed device was found to exhibit a promising sensing ability on paper devices without the need for sample pretreatment or bulky instrumentation, as normally required in conventional methods used for saliva analysis. An extensive linear dynamic range covering detection of salivary thiocyanate for both high and trace level regimes (5 orders of magnitude working range) was collectively achieved using the dual-sensing modes. Under optimal conditions, the limit of detection was 6 μmol L−1 with a RSD of less than 5%. An excellent stability for the μpumpPAD was also observed for over 30 days. Real sample analysis using the proposed device was found to be in line with the standard chromatographic method. Benefitting from simple fabrication and operation, portability, disposability, low sample volume (20 μL), and low cost (< 1 USD), the μpumpPAD is an exceptional alternative tool for the detection of various biomarkers in saliva specimens. [ABSTRACT FROM AUTHOR]