Novel Aggregation-Enhanced PEC Photosensitizer Based on Electrostatic Linkage of Ionic Liquid with Protoporphyrin IX for Ultrasensitive Detection of Molt-4 Cells

Nowadays, aggregation quenching of most organic photosensitizers in aqueous media seriously restricts analytical andbiomedical applications of photoelectrochemical (PEC) sensors. In this work, an aggregation-enhanced PEC photosensitizer wasprepared by electrostatically bonding protoporphyrin IX (PPIX) with an ionic liquid of 1-butyl-3-methylimidazole tetrafluoroborate([BMIm][BF4]), termed as PPIX-[BMIm] for clarity. The resultant PPIX-[BMIm] showed weak photocurrent in pure dimethylsulfoxide (DMSO, good solvent), while the PEC signals displayed a 44.1-fold enhancement in a water (poor solvent)/DMSO binarysolvent with a water fraction (fw) of 90%. Such PEC-enhanced mechanism was critically studied by electrochemistry and densityfunctional theory (DFT) calculation in some detail. Afterward, a label-free PEC cytosensor was built for ultrasensitive bioassay ofacute lymphoblastic leukemia (molt-4) cells by electrodepositing Au nanoparticles (Au NPs) on the PPIX-[BMIm] aggregates andsequential assembly of protein tyrosine kinase (PTK) aptamer DNA (aptDNA). The resultant cytosensor showed a wide linear range(300 to 3x105cells mL-1) with a limit of detection (LOD) as low as 63 cells mL-1. The aggregation-enhanced PEC performanceoffers a valuable and practical pathway for synthesis of advanced organic photosensitizer to explore its PEC applications in earlydiagnosis of tumors.

Automated summary

In this study, an aggregation-enhanced PEC photosensitizer PPIX-[BMIm] was prepared by electrostatic bonding, and its PEC performance in a binary solvent of water and DMSO was studied. A label-free PEC cytosensor was built using PPIX-[BMIm], which showed a wide linear range and low limit of detection for detecting leukemia cells.