Ultrasensitive amperometric determination of PSA based on a signal amplification strategy using nanoflowers composed of single-strand DNA modified fullerene and Methylene Blue, and an improved surface-initiated enzymatic polymerization.

The authors describe a signal amplification strategy for highly sensitive detection of the prostate-specific antigen (PSA). This is accomplished by a combination of two methods, viz. (a) improved surface-initiated enzymatic polymerization (SIEP), and (b) the use of nanoflowers prepared from C fullerene and Methylene Blue (C/MB) modified with a long single-strand DNA. C/MB acts as a novel electrochemical indicator. The C/MB nanoflowers improve the load of MB and promote the electron transfer. The integration of the SIEP technique and the C/MB nanomaterial also results in improved loading of MB on the nucleic acid. Ultimately, dual cascade signal amplification is accomplished. The biosensor was constructed as follows: (a) Gold nanospheres were modified with antibody 2 (Ab) and a thiolated oligonucleotide (referred to as S). (2) S is then extended by the SIEP reaction. (3) The redox indicator C/MB is then connected to the extended guanine-rich ssDNA which then yields the amperometric signal. (4) A sandwich immunoassay is performed by capturing the nanoprobe oy type Ab-Au-S on the gold electrode modified with multi-walled carbon nanotubes (MWCNTs) and protein A. Current is measured by using differential pulse voltammetry (DPV). The synergic effect of the biofunctional nanomaterial and the signal amplification strategy greatly improves the performance of this immunoassay. Under optimized conditions and at a working voltage of typically −0.18 V (vs Ag/AgCl), the assay has a linear range that extends from 15 pg·mL to 8 ng·mL of PSA. The detection limit is as low as 1.7 pg·mL (at an S/N ratio of 3). In our perception, this dual amplification scheme has a wide scope in that it may become applicable to numerous other immunoassays. [ABSTRACT FROM AUTHOR]