Long-Lived Charge Carriers in Mn-Doped CdS Quantum Dots for Photoelectrochemical Cytosensing

Photoelectrochemical (PEC) biosensing with semiconductor quantum dots (QDs) has received great attention because it integrates the advantages of both photo-excitation and electrochemical detection. During the photon-to-electricity conversion in PEC processes, electron-hole (charge) separation competes with electron-hole recombination, and the net effect essentially determines the performance of PEC biosensors. Herein, we propose a new approach for slowing down electron-hole recombination to increase charge separation efficiency for PEC biosensor development. Through doping with Mn2+, a pair of d bands (T-4(1) and (6)A(1)) is inserted between the conduction and valence bands of CdS QDs, which alters the electron-hole separation and recombination dynamics, allowing the generation of long-lived charge carriers with ms-scale lifetime that decay about 10(4)-10(5)-fold more slowly than in the case of undoped QDs. Photocurrent tests indicated that Mn2+ doping resulted in an approximately 80% increase in photocurrent generation compared with undoped CdS QDs. For application, the Mn-doped CdS QDs were coated on the surface of a glassy carbon electrode and functionalized with a cell surface carbohydrate-specific ligand (3-aminophenylboronic acid). In this way, a sensitive cytosensor for K562 leukemia cells was constructed. Moreover, the sugar-specific binding property of 3-aminophenylboronic acid allowed the electrode to serve as a switch for the capture and release of cells. This has been further explored with a view to developing a reusable PEC cytosensing platform.