Modified perylene diimide for femto molar level detection of glucose: smartphone-assisted colorimetric glucose detection kits

Abstract

In this report, a functionalized hydroxyphenyl benzothiazole (HBT) derivative has been synthesized and anchored onto the perylene diimide (PDI) core at the -bay position (PHI). PHI has been explored for the generation of radical anions (PH1˙⁻) and dianions (PH1²⁻) in 20% HEPES buffer–DMSO solution using H₂S as a sacrificial electron donor. The PH1˙⁻ has a half-life (t_1/2) of 1.5 h and 3 h in oxygenated and hypoxic conditions, respectively. The formation of radical anions has been confirmed by optical (absorbance and fluorescence) methods, cyclic voltammetry (CV), differential pulse voltammetry (DPV), and femtosecond transient absorbance spectroscopy along with current–voltage (I–V) and NOBF₄ studies. The PH1˙⁻ showed peroxidase-like activity for the reduction of H₂O₂ as low as 170 fmol L⁻¹ (fM) giving a colour change from sea green to pink. The biochemical assay which consists of PH1˙⁻+ GOx has been further utilized as a glucose sensor. Upon addition of glucose (0–8 nM) in the biochemical assay, the in-situ produced H₂O₂ (after oxidation of glucose with GOx) oxidized PH1˙⁻ to PH1 giving a sea green to pink colorimetric read out along with a decrease in the absorption intensities at 720, 815, 880 and 950 nm and the emergence of absorption intensity at 541 nm. The lowest limit of detection is 85 fM. We also explored this biochemical assay for the detection of 860 fM of glucose in a 10% blood serum. Similarly, fluorometric, CV and DPV studies were carried out for the detection of glucose using this biochemical assay. The smartphone-assisted RGB colour analyser showed large variations in the red colour and this RGB based colour differentiation can be used for the detection of 1 nM of glucose.