Abstract
A conjugated system was synthesized from reduced graphene quantum dot (rGQD) and hemin for the selective detection of favipiravir (Fav), an antiviral drug that has come into much attention during the year 2020 for its use as a drug against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The required rGQD was prepared from soot particles using Hummers' method followed by the amino-hydrothermal process. At the first step, its fluorescence was quenched by preparing the conjugate with hemin. Interestingly, the fluorescence intensity gradually increases (turn-on) with increasing concentration of Fav, and develops 9-fold higher fluorescence at 15.6 nM of Fay. The fluorescence enhancement is selective, and the limit of detection (LOD) was calculated to be about 1.96 nM. The fluorescence turnon is governed by aggregation-induced emission (ME), which originates from electrostatic interactions between the sensor-analyte systems. A similar fluorescence turn-on was observed for Fav in human blood plasma (BP) as well as in artificial urine (AU), which indicates that the sensor is viable in real-sample analysis. In addition to Fav, its 1:1 cocrystals with theophylline (Theo) and ferulic acid (FRA) also enhance the fluorescence in real samples with an LOD of 3.47 and 12.2 nM, respectively. Therefore, the cocrystals remain intact in biological medium and the sensor interacts with cocrystals too. The detection of Fav and its cocrystals, and the development of cocrystals as alternatives in the pharmaceutical industry, is essential considering the current COVID-19 pandemic worldwide. Therefore, the findings of this work will certainly help in developing fluorescence sensors for quantitative determination of active pharmaceutical ingredients (APIs) in real samples.