Differential and comparative sensing modes of AIS and AIS@ZnS core-shell quantum dots towards bioanalytes

Herein, we propose a quantum dots (QDs) based spectroscopic sensor for determination of ascorbic acid, gallic acid and oxalic acid. These aqueous stable AgInS₂ (AIS) and AIS@ZnS QDs having average sizes of 2.5 ± 0.5 and 3.4 ± 0.5 nm, respectively, were surface coated with Glutathione (GSH), which provided enhanced stability against the aggregation/oxidation. These glutathione (GSH) capped AIS and AIS@ZnS core-shell nanostructures were systematically studied as a luminescence probe for the sensing of routinely used analytes. AIS QDs exhibit better specificity and selectivity for ascorbic acid and gallic acid detection, whereas, core-shell QDs show higher binding affinity and sensing ability for oxalic acid. It was noticed that AIS QDs exhibited 80% quenching efficiency towards gallic acid, compared to 55% of AIS@ZnS QDs. In addition, AIS QDs shows threefold increment in binding affinity towards gallic acid compared to AIS@ZnS nanostructures. As the consequence, AIS and AIS@ZnS QDs show concentration dependent red-shifted after binding with analytes. Based on this, AIS@ZnS QDs was found highly sensitive for the detection of oxalic acid with excellent detection limit as 35 nM. Interestingly, AIS QDs shows the specific and selective binding towards gallic acid where fluorescence quenching was noted and ascorbic acid for which fluorescence enhancement was observed. It was noted that these QDs shows the detection limit as 20 nM for GA and 45 nM for AA. Based on this, AIS and AIS@ZnS QDs can be used as fluorescence tool for multimode sensing of gallic acid ascorbic acid and oxalic acid with high selectivity and sensitivity.