Addressable Label-Free Photoelectric Sensor Array with Self-Calibration for Detection of Neuron Specific Enolase.

An addressable label-free photoelectric immunosensor array was designed for detection of neuron specific enolase (NSE) based on TiO2/CdS as substrate materials. In this work, the hydrothermal synthesized TiO2 nanorod film is evenly grown on the surface of the fluorine-doped tin oxide (FTO), and then CdS with a narrow band gap is added for sensitization through successive ionic layer adsorption reactions. The obtained TiO2/CdS composite materials with matched energy band structures promote the rapid electron transfer and effectively reduce the recombination of electron hole pairs, which greatly enhance the visible light absorption and increased photocurrent intensity. In order to construct a suitable sensor array, the sensitized FTO electrode is divided into multiple regions of equal size by insulating stickers, and then the addressable and continuous detection of multiple samples can be achieved. Because multiple detection regions are prepared and tested under the same conditions, the difference effectively reduces, and the sensor can realize self-calibration and obtain more accurate results. Under optimal conditions, this sensor array can detect NSE in the linear range of 0.01-100 ng mL-1 with a detection limit of 2.49 pg mL-1 (S/N = 3). The sensor array has good selectivity, stability, and reproducibility, making it a viable approach for real sample detection.

Enzyme-Free Colorimetric Immunoassay for Protein Biomarker Enabled by Loading and Disassembly Behaviors of Polydopamine Nanoparticles.

In this work, a mussel-inspired polydopamine (PDA) nanoparticle with biocompatible and reactive surface characteristics was desirably incorporated with high loading capacity and pH-induced disassembly-releasing behavior toward Fe(III) ions to develop an enzyme-free colorimetric immunoassay. The catechol functional network of PDA can act as a scaffold to coordinate with large amounts of Fe(III) ions to form the PDA-Fe(III) NPs whose coordination state can be tailored by changing the pH values. In detail, PDA-Fe(III) NPs can be maintained in a disassembled tri-coordinate state under alkaline conditions while the highly loaded Fe(III) ions can be easily released under acid conditions to react with ferrocyanide for the in situ generation of Prussian blue (PB) NPs. The detection sensitivity of prostate-specific antigen (PSA) was significantly improved, owing to the high peroxidase-like activity of PB NPs that triggered excellent catalytic effect by the colorimetric reaction. In addition, favorable linearity was found in the range of 0.0005-20 ng mL-1 with a low detection limit of 0.84 pg mL-1 (S/N = 3). Furthermore, excellent selectivity and reproducibility were exhibited by the developed enzyme-free colorimetric immunoassay. It is believed that this proposed PDA-Fe(III) NP-based enzyme-free colorimetric system will offer a facile and reliable tool for the sensitive detection of PSA and other cancer biomarkers in human serum.

Ultrasensitive immunosensor for prostate specific antigen using biomimetic polydopamine nanospheres as an electrochemiluminescence superquencher and antibody carriers.

In this work, biomimetic polydopamine nanospheres (PDANSs) were easily prepared and were firstly exploited as an electrochemiluminescence (ECL) nanoquencher for the development of a sandwich type immunosensor. The PDANSs with abundant active functional groups can facilely label the detection antibody and show remarkable quenching effect towards the ECL of the tris-(2,2'-bipyridine)ruthenium (Ru(bpy)32+). The amino-modified multiwall carbon nanotubes/Nafion (MWCNTs-NH2@N) composite-film was adopted as a matrix to incorporate the luminophor Ru(bpy)32+ and immobilize the capture antibody. The prominent decrease of ECL signal intensity was obtained on account of the unique quenching ability of the labeled PDANSs. The quenching mechanism is believed that the excited states of Ru(bpy)32+ can be annihilated by quinone units in PDANSs via energy transfer. The ECL quenching efficiency was logarithmically related to the concentration of the prostate specific antigen (PSA) in the range from 0.1 pg mL-1 to 20 ng mL-1 with a detection limit of 35 fg mL-1. Furthermore, the proposed ECL immunosensor presented good stability, repeatability and selectivity.