Atomically precise pieces of matter of nanometer dimensions composed of noble metals are new categories of materials with many unusual properties. Over 100 molecules of this kind with formulas such as Au25(SR)18, Au38(SR)24, and Au102(SR)44 as well as Ag25(SR)18, Ag29(S2R)12, and Ag44(SR)30 (often with a few counterions to compensate charges) are known now. They can be made reproducibly with robust synthetic protocols, resulting in colored solutions, yielding powders or diffractable crystals. They are distinctly different from nanoparticles in their spectroscopic properties such as optical absorption and emission, showing well-defined features, just like molecules. They show isotopically resolved molecular ion peaks in mass spectra and provide diverse information when examined through multiple instrumental methods. Most important of these properties is luminescence, often in the visible–near-infrared window, useful in biological applications. Luminescence in the visible region, especially by clusters prot...

Atomically Precise Clusters of Noble Metals: Emerging Link between Atoms and Nanoparticles

We review the progress achieved during the recent five years in immunochemical biosensors (immunosensors) combined with nanoparticles for enhanced sensitivity. The initial part introduces antibodies as classic recognition elements. The optical sensing part describes fluorescent, luminescent, and surface plasmon resonance systems. Amperometry, voltammetry, and impedance spectroscopy represent electrochemical transducer methods; electrochemiluminescence with photoelectric conversion constitutes a widely utilized combined method. The transducing options function together with suitable nanoparticles: metallic and metal oxides, including magnetic ones, carbon-based nanotubes, graphene variants, luminescent carbon dots, nanocrystals as quantum dots, and photon up-converting particles. These sources merged together provide extreme variability of existing nanoimmunosensing options. Finally, applications in clinical analysis (markers, tumor cells, and pharmaceuticals) and in the detection of pathogenic microorganisms, toxic agents, and pesticides in the environmental field and food products are summarized.

Nanoparticle-Based Immunochemical Biosensors and Assays: Recent Advances and Challenges

Owing to their excellent multiplexing ability, high sensitivity, and large dynamic range, immunoassays using surface-enhanced Raman scattering (SERS) as the readout signal have found prosperous applications in fields such as disease diagnosis, environmental surveillance, and food safety supervision. Various ever-increasing demands have promoted SERS-based immunoassays from the classical sandwich-type ones to those integrated with fascinating automatic platforms (e.g., test strips and microfluidic chips). As recent years have witnessed impressive progress in SERS immunoassays, we try to comprehensively cover SERS-based immunoassays from their basic working principles to specific applications. Focusing on several basic elements in SERS immunoassays, typical structures of SERS nanoprobes, productive optical spectral encoding strategies, and popular immunoassay platforms are highlighted, followed by their representative biological applications in the last 5 years. Moreover, despite the vast advances achieved ...

SERS-Activated Platforms for Immunoassay: Probes, Encoding Methods, and Applications

Direct, label-free detection of unmodified DNA is a great challenge for DNA analyses. Surface-enhanced Raman spectroscopy (SERS) is a promising tool for DNA analyses by providing intrinsic chemical information with a high sensitivity. To address the irreproducibility in SERS analysis that hampers reliable DNA detection, we used iodide-modified Ag nanoparticles to obtain highly reproducible SERS signals of single- and double-strand DNA in aqueous solutions close to physiological conditions. The phosphate backbone signal was used as an internal standard to calibrate the absolute signal of each base for a more reliable determination of the DNA structure, which has not been achieved before. Clear identification of DNA with single-base sensitivity and the observation of a hybridization event have been demonstrated.

Label-Free Surface-Enhanced Raman Spectroscopy Detection of DNA with Single-Base Sensitivity

Recent advances in biosensor development for the detection of cancer biomarkers

Gold and silver nanoparticles (Au/AgNPs) are widely used in analytical chemistry, and their intense colors have inspired artists and fascinated scientists. This review describes the absorption and Rayleigh-scattering effects of the surface-plasmon resonance (SPR) of Au/AgNPs. Specifically, the color associated with Au/AgNPs is utilized for immunoassay and aptamer assays. SPR-Rayleigh scattering is used for nanoanalysis, when combined with immune, aptamer and nanocatalysis reactions.

The surface-plasmon-resonance effect of nanogold/silver and its analytical applications

As an important analysis technology, SERS has the characteristics of fast, sensitive, informative and highly selective. The sensitivity and reproducibility are highly dependent on the properties of SERS substrate, thus it is a study hotspot in SERS quantitative. Although solid phase substrates are widely and early utilized in SERS detection, there are some problems in reproducibility and accuracy and complicated drying process. With development of nanotechnology, facile, highly SERS active, stable and reproducible nanosol substrates were prepared that overcome the problems and fills the gap in this area and expands the application field of SERS quantitative analysis. Using nanoenzyme and bioenzyme catalysis of nanoparticle and molecular reactions to amplify SERS signal, and aptamer to improve the selectivity, some highly sensitive and selective nanosol SERS quantitative analysis methods have been developed with good accuracy. Combining with the work of our group, this paper summarizes the progress of SERS quantitative analysis.

Nanosol SERS quantitative analytical method: A review

The stable silver nanorod (AgNR) sol in red was prepared by the two-step procedure of NaBH4-H2O2 and citrate heating reduction. The AgNR had a transverse and a longitudinal surface plasmon resonance (SPR) absorption peak at 338 nm and 480 nm. Meanwhile, two transverse and longitudinal SPR Rayleigh scattering (SPR-RS) peaks at 340 nm and 500 nm were observed firstly using common fluorescence spectrometer. The SPR absorption, RS, surface enhanced Raman scattering (SERS) and electron microscope technology were used to study the formation mechanism of red silver nanorods and the SERS enhancement mechanism of nano-aggregation. The AgNR-BPO SPR absorption and AgNR-NaCl-BPO SPR-RS analytical systems were studied to develop two new simple, rapid and low-cost SPR methods for the detection of trace BPO.

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A new silver nanorod SPR probe for detection of trace benzoyl peroxide

In pH 4.4 HAC–NaAC buffer solution at 80 °C, nanogold particles (NG) strongly enhanced the slow, colored reaction of Ag(I)–gallic acid to form nanosilver particles, which exhibited a strong surface plasmon resonance (SPR) absorption peak at 460 nm, but the aggregated nanogold particles (ANG) exhibited a weak enhancement. The increased absorption value at 460 nm was linear to the NG concentration in the range of 3.6–72.5 ng mL−1 Au. In pH 5.5 MES buffer solution at 80 °C, single-stranded substrate DNA and DNAzyme hybridize to form double-stranded DNA (dsDNA). The presence of uranyl (UO22+) resulted in cleavage of the substrate DNA of dsDNA, releasing a short, single-stranded DNA that can be adsorbed onto the NG and protect them from aggregation; those un-adsorbed NG were aggregated to ANG. As the UO22+ concentration increased, more short, single-stranded DNA were released, and more NG were protected by the cleavage of substrate single-strand DNA, so the colored particle reaction and the absorption value at 460 nm enhanced linearly. On those grounds, 0.083–0.67 nmol L−1 UO22+ can be detected rapidly by this colorimetric sensing assay, with a detection limit of 0.04 nmol L−1.

Colorimetric sensing of trace UO22+ by using nanogold-seeded nucleation amplification and label-free DNAzyme cleavage reaction

The stable reduced graphene oxide/triangular plate-type nanosilver aggregation/rhodamine 6G (rGO/TAgA/Rh6G) nanosensor exhibited a strong surface-enhanced Raman scattering (SERS) peak at 1505 cm −1 that was used to monitor the Rh6G concentration changes in the nitrosation reaction between Rh6G and NO 2 − , in which NO 2 − increase results in the SERS intensity decrease due to the decreasing Rh6G. The decreased SERS intensity was linear to nitrite concentration in the range of 0.7–72 nmol/L, with a detection limit of 0.2 nmol/L. Nitrite in water samples was analyzed by this Rh6G SERS nanosensor, with recovery of 94.8%–108% and relative standard deviation of 4.4%–7.5%.

Guiqing Wen

Papers

The surface-plasmon-resonance effect of nanogold/silver and its analytical applications

Nanosol SERS quantitative analytical method: A review

A new silver nanorod SPR probe for detection of trace benzoyl peroxide

Colorimetric sensing of trace UO22+ by using nanogold-seeded nucleation amplification and label-free DNAzyme cleavage reaction

SERS detection of trace nitrite ion in aqueous solution based on the nitrosation reaction of rhodamine 6G molecular probe