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 Mn(2+) , a pair of d bands ((4) T1 and (6) A1 ) 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 Mn(2+) 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.