Multiplexed headspace paper-based analytical devices modified with silver nanoclusters for smartphone-based...

Reliable determination of inorganic chemical preservatives is essential for ensuring food safety, due to the health concerns associated to these compounds when present at excessive levels. Nitrite and sulfite, two inorganic preservatives widely used in the food industry, increasingly demand miniaturized alternatives to conventional analytical methods. In this regard, luminescent nanosensors are of particular relevance because of their superior sensitivity. However, further improvements are still needed to enhance their selectivity and multiplexing capability, while ensuring their applicability in the analysis of complex matrices.

The present study reports on the development of two paper-based analytical devices (PADs) involving luminescent silver nanoclusters (AgNCs) as sensing nanoreceptors for the simultaneous smartphone-assisted detection of sulfite and nitrite. The assays rely on the highly selective recognition of nitrogen oxides and sulfur dioxide by AgNCs protected with poly(methacrylate) and polyethylenimine, respectively, separately immobilized in the detection areas of PADs. Thus, in this work, AgNCs-containing PADs have been devised for the simultaneous determination of sulfite and nitrite involving in situ formation of the volatile derivatives and their selective trapping/interaction with the corresponding AgNCs nanoreceptors, leading to luminescence quenching. Two different configurations have been evaluated for the development of PAD-based nanosensors, namely in-vial PAD-based headspace microextraction (HS-PAD) and headspace 3D origami microfluidic PAD (HS-μPAD). Under optimal conditions, the developed assays showed limits of detection as low as 0.29 μM and 0.23 μM for sulfite and nitrite, respectively, for the HS-PAD approach, and 1.9 μM and 3.2 μM for the HS-μPAD configuration, with a repeatability expressed as relative standard deviation lower than 7.3 % (N = 8) in all cases. In addition, the developed PAD-based nanosensors were applied to the analysis of food samples, the results obtained showing excellent agreement with those obtained with reference methods.

This article reports, for the first time, on the assessment of AgNCs with different responsiveness as luminescent nanoprobes for the development of multiplexed paper-based nanosensors with headspace sampling. The proposed assays enable decentralized, affordable and straightforward detection of sulfite and nitrite, being complementary in terms of sample consumption and sensitivity, and represent advantageous alternatives for quality control and safety monitoring in the food industry.