Enhanced Near-Infrared Electrochemiluminescence from Trinary Ag-In-S to Multinary Ag-Ga-In-S Nanocrystals via Doping-in-Growth and Its Immunosensing Applications.

Screening toxic-element-free and biocompatible electrochemiluminophores was crucial for electrochemiluminescence (ECL) evolution. Herein, l-glutathione (GSH)-capped Ag-Ga-In-S (AGIS) nanocrystals (NCs) were prepared by doping Ag-In-S (AIS) NCs in a doping-in-growth way and utilized as a model for both ECL modulating and developing multinary NC-based electrochemiluminophores with enhanced ECL performance than trinary NCs. AGIS NCs not only primarily preserved the morphology, size, phase structure, and water monodisperse characteristics of AIS NCs with broadened band gap but also demonstrated obviously enhanced oxidative-reduction ECL than AIS NCs. Importantly, ECL of AGIS NCs was located at the near-infrared region with a maximum emission wavelength of 744 nm and could be utilized for an ECL immunoassay with human prostate-specific antigen (PSA) as a model, which exhibited a linearity range from 0.05 pg/mL to 1.0 ng/mL and a low limit of detection of 0.01 pg/mL (S/N = 3). This work provided a promising alternative to the traditional binary NCs for developing toxic-element-free and biocompatible electrochemiluminophores with efficient near-infrared ECL.

Electrochemically Lighting Up Luminophores at Similar Low Triggering Potentials with Mechanistic Insights.

Electrochemiluminescence (ECL) with high electrode compatibility and less electrochemical interference has conventionally been envisioned by lowering the oxidative potential of luminophores and/or screening luminophores with a low oxidative potential. Herein, an alternative was developed by employing the environmental-friendly carbohydrazide as a coreactant, which enabled serial luminophores with oxidative-reduction ECL at one similar low triggering potential around 0.55 V versus Ag/AgCl, including Ru(bpy)32+ as well as CdTe, CdSe, CuInS2/ZnS, and Au nanocrystals. Because the eight-electron releasing process of carbohydrazide was electrochemically triggered at ∼0.25 V versus Ag/AgCl, the radicals generated via electrochemical oxidation of carbohydrazide could reduce the luminophores at a much lower potential than those of traditional coreactants. All the luminophore/carbohydrazide systems exhibited one ECL process around 0.55 V, which was about 0.65 V lower than that of a traditional Ru(bpy)32+/tri-n-propylamine system (typically around +1.2 V), and even lower than the oxidative potential of some luminophores. The ECL of the luminophore/carbohydrazide system was spectrally close to that of the corresponding luminophore/tri-n-propylamine system; the maximum emission wavelength of the low triggering potential ECL could shift from 540 to 783 nm via the selection of luminophores in this case. The coreactant screening strategy would be a favorable addition to the expected luminophore screening strategy for achieving enhanced ECL performance. This work created an avenue toward a deeper understanding of the ECL mechanism.

Promising Electrochemiluminescence from CuInS2/ZnS Nanocrystals/Hydrazine via Internal Cu(I)/Cu(II) Couple Cycling.

Screening a novel electrochemiluminescence (ECL) system is crucial to ECL evolution. Herein, an efficient ECL system with less interference and environmental concern under physiological condition is developed via a unique internal Cu(I)/Cu(II) couple cycling amplified strategy by employing the glutathione- and citrate-capped copper indium sulfide (CIS)/ZnS nanocrystals (NCs) as electrochemiluminophore and N2H4·H2O as co-reactant. CIS/ZnS NCs can be electrochemically injected with valence band (VB) hole at 0.46 and 0.87 V (vs Ag/AgCl), and then achieve the same hole-injected states by relocalizing VB holes with the Cu(I) species inside of CIS/ZnS NCs to form internal Cu(II) defects, while each N2H4·H2O molecule can be successively oxidized to two more reducing species N2H3• and N2H2 around 0.10 V, and inject conduction band (CB) electron onto CIS/ZnS NCs for triple times. The internal Cu(I)/Cu(II) couple cycling involved radiative-charge recombination between these VB hole and CB electron eventually enables two efficient near-infrared ECL processes (around 731 nm) at 0.55 and 0.87 V, in which each single nanocrystal may participate in multiple ECL reaction cycles to produce multiple photons for amplified ECL, similar to the tris(bipyridyl)ruthenium(III) based ECL system. The low-triggering-potential ECL process at 0.55 V can be utilized to selectively determine Cu(II) with a wide linear range from 10 and 1500 nM and a limit of detection of 5 nM (S/N = 3). This work presents a NCs engineering and co-reactant selecting combined strategy for further ECL evolution.

Efficient and Monochromatic Electrochemiluminescence of Aqueous-Soluble Au Nanoclusters via Host-Guest Recognition.

Inspired by the enhanced photoluminescence of Au nanoclusters (AuNCs) with a rigid shell, the formation of rigid host-guest assemblies on AuNC surfaces was employed to screen novel electrochemiluminophores with 6-aza-2-thiothymine(ATT)-protected AuNCs (ATT-AuNCs) and l-arginine (ARG) as models for the first time. The rigid host-guest assemblies formed between ARG and ATT on the ATT-AuNC surface enabled aqueous-soluble ARG/ATT-AuNCs with a dramatically enhanced electrochemiluminescence (ECL) compared to ATT-AuNCs. This includes one cathodic ECL process (-1.30 V) and three anodic ECL processes (+0.78, 0.90, and 1.05 V) in a so-called half-scan experiment without a co-reactant, as well as a 70-fold enhanced oxidative-reduction ECL at +0.78 V with tri-n-propylamine as a co-reactant. Importantly, the ECL of the ARG/ATT-AuNCs is highly monochromatic with an emission maximum around 532 nm and a full width at half-maximum of 36 nm, which is of great interest for color-selective ECL assays.

Red-shifted electrochemiluminescence of CdTe nanocrystals via Co2+-Doping and its spectral sensing application in near-infrared region.

Novel optical labels for biosensing in near-infrared (NIR) region (especially between 800 and 900 nm) are arousing much attention for higher penetrating capability, less scattering and lowered autofluorescent background. Herein, a water-soluble electrochemiluminophore with effective electrochemiluminescence (ECL) around 815 nm is developed via doping dual-stabilizers-capped CdTe nanocrystals (NCs) with Co2+ species in a growth-doping way. The Co2+-doped CdTe NCs not only can preserve the highly-passivated surface states of dual-stabilizers-capped CdTe NCs, but also exhibit efficient red-shifted photoluminescence (PL) and ECL into the promising optical NIR window of 800-900 nm. A spectrum-based ultrasensitive NIR ECL immunosensor is consequently fabricated with the Co2+-doped CdTe NCs as tags for the first time, which can selectively and sensitively determine human carcinoembryonic antigen with a wide linearity range from 1 fg/mL to 10 pg/mL and a low limit of detection at 0.2 fg/mL (S/N = 3). This work opens a way to screen novel NIR electrochemiluminophore as well as to modulate the ECL performance of NCs via surface doping and engineering.

Dual-wavebands-resolved electrochemiluminescence multiplexing immunoassay with dichroic mirror assistant photomultiplier-tubes as detectors.

A dual-wavebands-resolved electrochemiluminescence (ECL) multiplexing immunoassay (MIA) was developed for simultaneously detecting alpha fetoprotein antigen (AFP) in greenish waveband with CdSe550 (λmax = 550 nm) nanocrystals (NCs) and carbohydrate antigen 125 (CA125) in near-infrared waveband with CdTe790 (λmax = 790 nm) NCs via one-pot ECL reaction, in which dichroic mirror works as a key part to reflect ECL from CdSe550 to one photomultiplier-tube (PMT) and transmit ECL from CdTe790 to the other PMT for dual-wavebands-resolved assay. The proposed ECL-MIA strategy was capable of simultaneously determining AFP with linearly response from 5 pg/mL to 5 ng/mL and limit of detection at 1 pg/mL, and CA125 with linearly response from 5 mU/mL to 1 U/mL and limit of detection at 1 mU/mL, with desired specificity and without obvious energy-transfer between ECL tags. The dichroic mirror assistant ECL setup is easy-to-assemble and convenient for the popularization of color-resolved multiplexing ECL assay.