Abstract
<jats:p>The rapid detection of emerging water contaminants at ultra trace concentrations remains a major challenge in environmental analytical chemistry. This study presents a graphene quantum dot (GQD)–MXene nano-optoelectronic interface as a high-performance photoelectrochemical (PEC) sensing platform for the ultrasensitive determination of representative pharmaceutical contaminants, including ciprofloxacin (CIP), sulfamethoxazole (SMX), and diclofenac (DCF). The GQD–MXene heterointerface significantly enhances visible-light absorption, promotes interfacial charge separation, and accelerates electron transport, resulting in a 4.8-fold increase in photocurrent density (from 13.2 to 63.7 μA cm-2) under AM 1.5G illumination (100 mW cm-2). Electrochemical impedance spectroscopy revealed a low charge-transfer resistance of 38.6 Ω, compared with 214.5 Ω for pristine MXene, while photoluminescence quenching reached 82.4%, confirming efficient suppression of electron–hole recombination. Under optimized experimental conditions, the PEC sensor exhibited a wide linear response from 10 fM to 10 μM (R2 = 0.9989) for ciprofloxacin, with a detection limit of 3.2 fM (S/N = 3) and a sensitivity of 9.86 μA μM-1 cm-2. Corresponding detection limits of 5.8 fM and 7.1 fM were achieved for sulfamethoxazole and diclofenac, respectively. The sensor demonstrated excellent selectivity against 100-fold excess concentrations of common inorganic ions (Na+, K+, Ca2+, Mg2+, Cl-, SO42- and NO3-), humic acid, glucose, and ascorbic acid, with signal variations below 4.3%. Repeatability and reproducibility were satisfactory, with relative standard deviations of 2.6% (n = 10) and 3.4% for independently prepared electrodes. After 30 days of storage at 4 °C, the sensor retained 95.1% of its initial photocurrent response. The analytical applicability of the GQD–MXene PEC interface was validated using river, tap, and wastewater effluent samples, achieving recoveries ranging from 96.8% to 103.4% with relative standard deviations below 3.8%. These results demonstrate that the GQD–MXene nano-optoelectronic interface provides exceptional analytical performance for photoelectrochemical sensing and represents a promising platform for portable, rapid, and ultrasensitive environmental monitoring of emerging water contaminants.</jats:p>