Electrochemical immunosensor for ultra-sensitive detection of attomolar prostate specific antigen with sulfur-doped graphene quantum dot@gold nanostar as the probe

A novel sulfur-doped graphene quantum dot (S-GQD) decorated 3-dimensional gold nanostar (AuNS/S-GQD) nanocomposite has been developed as the actively electrochemical immunosensing material for ultra-sensitive and selective detection of attomolar prostate specific antigen (PSA) in phosphate buffer saline (PBS) and human serum. The S-GQDs were hydrothermally prepared at 180 °C for 10 h, and then AuNS/S-GQDs were fabricated by reducing Au precursor to AuNS in the presence of S-GQDs at room temperature. The electronic microscopic results indicate that 2 – 8 nm S-GQDs are homogenously deposited onto the 35 – 60 nm AuNS surface. The AuNS provides an excellent electric conductivity for electrochemical performance, while S-GQD serves as a sensing probe to bind prostate specific antibody (Ab) via amide bonding. After deposition of AuNS/S-GQDs onto screen-printed electrode (Es), the Es||AuNS/S-GQD/Ab immunosensor provides a stable, ultra-sensitive, and highly selective platform for PSA detection. The wide detection ranges of 10 fg mL⁻¹ – 50 ng mL⁻¹ and 100 fg mL⁻¹ – 35 ng mL⁻¹ with low limits of detection (LOD) of 0.29 (9.7 aM) and 26 fg mL⁻¹ in PBS and neat human serum, respectively, are obtained. Moreover, the Es||AuNS/S-GQD/Ab immunosensor can effectively detect PSA in human serum with recovery of 97 – 107%. The high selectivity toward PSA detection over the other 8 interferences and low cytotoxic effect of Es||AuNS/S-GQD/Ab immunosensor are also observed. These excellent results demonstrate the potential of using AuNS/S-GQD nanocomposite as an electrochemically biosensing probe to effectively detect PSA and other cancer markers in human serum for clinically early diagnosis.