The overwhelming majority of commercially available chemiluminescence (CL) assays are conducted in the eye-visible region. Herein, a near-infrared (NIR) aqueous CL strategy was proposed with CuInS2@ZnS nanocrystals (CIS@ZnS NCs) as emitters. Hydrazine hydrate (N2H4·H2O) could inject electrons into the conduction band of the CIS@ZnS NCs and simultaneously transformed to the intermediate radical N2H3 •. N2H3 • reduced dissolved oxygen (O2) to O2 –•, while the O2 –• could inject holes into the valence band of the CIS@ZnS NCs. The recombination of electrons and holes at Cu+ defects in CIS@ZnS NCs eventually yielded efficient NIR CL at around 824.1 nm, which is the longest waveband for NCs CL to the best of our knowledge. The NIR CL could be conveniently performed in the neutral aqueous medium (pH 7.0) with a quantum yield of 0.0155 Einstein/mol and was successfully employed for constructing a signal-off CL biosensor with ascorbic acid as the analyte as well as a signal-on CL biosensor for determining ascorbate oxidase, which indicates that this NIR CL system has a promising potential for bioassays in diverse ways.

A simple and highly sensitive photoelectrochemical (PEC) immunoassay sensor was fabricated by using the two forms of polydopamine (PDA), the thin film and nanosphere, to serve as the photoelectrode-modified material and signal reporting label, respectively. The two forms of PDA show similar light absorption behavior but totally different PEC activities. The PDA film can extend the light absorption from the ultraviolet to near infrared light range, transfer a photoelectron to TiO2 nanoparticles and the underlying photoelectrode, and largely amplify the photocurrent response. However, the PDA nanospheres have insignificant photoelectron transport ability. When they are brought close to the PDA film and TiO2 nanocomposite-modified electrode via the sandwich immunoreaction, they function like a black hole to compete with the PDA film for light absorption, resist the access of the electron donor to regenerate the photoactive material, and capture the photoelectron generated from the PDA film. Besides, the heat generated from the PDA nanospheres also contributes to the photocurrent decrease. The PDA nanospheres with multiple quenching effects on the PDA film greatly decrease the photocurrent signal and lead to a highly sensitive PEC immunosensing strategy. Under optimal conditions, a wide linear range from 0.1 to 106 pg·mL–1 is obtained toward carcinoembryonic antigen, with a low limit of detection of 40 fg·mL–1. Besides, the PDA with excellent biosafety can be readily assembled with proteins, which thus simplifies the preparation procedures and decreases the costs. All these features indicate that the whole PDA-based PEC sensing strategy may have great application prospects for the point-of-care assay of various kinds of tumor markers.

Fluorescence ratiometric biosensors are valuable tools for the accurate and sensitive prediction and diagnosis of diseases. However, seldom have fluorescence ratiometric biosensors for protein and DNA been reported because of the shortage of suitable nanoscale scaffolds. Herein, a tripyridinyl Ru II complex− encapsulated SiO 2 @polydopamine (Ru−SiO 2 @PDA) nanocomposite was designed as a universal platform for fluorescence ratiometric detection of DNA and protein in serum samples. The Ru−SiO 2 @PDA nanocomposites have a narrow size distribution, exhibit good biosafety, and are convenient for the postmodification of biorecognition elements. Under irradiation, they can emit a stable and strong luminescence at 650 nm and simultaneously quench the fluorescence emitted from the fluorophores getting close to them. Once the capture probes such as single-stranded DNA and aptamer are assembled, the fluorophores labeled on them are then brought close to their PDA shell and quenched. However, the biorecognition behaviors change the probe's configuration and take the fluorophore far away from the PDA shell. Correspondingly, the fluorescence recovers and its ratio to the constant fluorescence reference is linear to the targets' concentration. Using a D-catalyst and thrombin as model analytes, the Ru−SiO 2 @PDA-based nanoplatform shows high sensitivity and good accuracy in the serum sample analysis. Regarding these attractive properties, the Ru− SiO 2 @PDA nanoplatform provides a new avenue for the accurate and sensitive fluorescence assay of a wide range of targets in complex systems.