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A simple magnetic electrochemical aptasensor was established for the detection of prostatic specific antigen (PSA). Ag/CdO nanoparticles (NPs) were fabricated and exhibited strong electroreduction peaks at −1.07 V, attributing to the electron transfer from Cd2+ to Cd0 and the superior electron transportation of Ag. Aptamer-modified Ag/CdO NPs were assembled on the surface of superparamagnetic Fe3O4/graphene oxide nanosheets (GO/Fe3O4 NSs) through the hydrophobic and π–π stacking interaction of aptamers and GO NSs. These assemblies possessed superior electroactive properties, efficient electron transfer, and superparamagnetic response and could serve as sensing units for PSA detection with the aid of a magnetic electrode. With increasing concentrations of PSA, the high affinity of aptamers to PSA enabled the dissociation of Ag/CdO NPs from GO/Fe3O4 NSs, decreasing the intensity of electroreduction peaks. The Ag/CdO NP-engineered magnetic electrochemical aptasensor achieved sensitive and accurate detection of PSA in the range of 50 pg/mL to 50 ng/mL. The limit of detection (LOD) was as low as 28 pg/mL. This developed protocol can be extended to a large set of strong electroactive labels for reliable tumor biomarker detection with high sensitivity and specificity.

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A novel ingenious and ultrasensitive chiral electrochemical transducer is proposed for tryptophan (Trp) isomer detection by using electroactive Au@Ag NPs as electrochemical tags. Moreover, the large binding constant of d-Trp on NPs and strong interaction between d-Trp and Cu2+ cause electroactive Au@Ag NP to assemble on the electrode, generating strong differential pulse voltammetry (DPV) signals from the oxidation of Ag0 to Ag+. In sharp contrast to d-Trp, l-Trp leads to the assembly of Au@Ag NP oligomers on the electrode, resulting in a weak DPV signal. The distinct DPV responses enable the developed electrochemical chiral transducer for the sensitive and accurate quantification of d-/l-Trp. The limit of detection (LOD) is 1.21 pM for d-Trp. This established electrochemical chiral sensor also achieves the specific determination of enantiomeric excess. In comparison to other reported approaches, this proposed electrochemical chiral sensor excels by its sensitivity, simplicity, and good availability of electroactive Au@Ag NP assemblies. Target-induced colorimetric assays can be converted into electrochemical assays for the dual signal amplification in the field of ultrasensitive enantioselective chiral discrimination.

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