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Plasmon-enhanced light harvesting has been of great interest to enhance the catalytic efficiency of some composites or hybrids. The enhanced peroxidase-like activity of phosphorylated iron(III) porphyrin (TPPFe(III))-based nanocomposite, induced by localized surface plasmon resonance for a colorimetric assay, was developed in this study. Firstly, a phosphate group modification strategy was adopted to synthesize water-soluble iron(III) porphyrin materials. Then, the as-synthesized TPPFe(III) was covalently attached to core-shell gold nanorods (GNRs), GNR@Au 2 S/AuAgS, to form TPPFe(III)-GNR@Au 2 S/AuAgS nanocomposite, which shows greatly enhanced peroxidase-like activity compared to TPPFe(III). A mechanism for the enhanced peroxidase-like activity of TPPFe(III)-GNR@Au 2 S/AuAgS was proposed, which results from a synergic effect of hot electrons excited by localized surface plasmon resonance and photogenerated electrons of the TPPFe(III), verified by experiments. Furthermore, a fast colorimetric assay for the detection of H 2 O 2 and glucose was established based on the unique property of TPPFe(III)-GNR@Au 2 S/AuAgS. This colorimetric assay was applied to determine practical human serum samples; satisfactory results demonstrate this method has high accuracy. The present study would not only provide some insights into the mechanism of plasmon-activated enzyme-like reactions, but also offer new strategies for improving the catalytic activity of a mimetic enzyme.

A biosensor based on localized surface plasmon resonance (LSPR) was developed to detect the antibody of Mycobacterium tuberculosis using the fusion protein CFP10-ESAT6 as an antigen. To explore the diagnostic potential of the biosensor for tuberculosis (TB), the fusion protein CFP10-ESAT6 was immobilized on gold nanorods (Au NRs) by chemical modification, and the functionalized Au NRs were subsequently incubated with serums collected from TB patients, non-tuberculous pulmonary disease patients or healthy individuals. The change in the LSPR properties of Au NRs from the specific interaction between the antigen and antibody was monitored, and detection of the target antibody was completed based on the proposed biosensor. Serum analysis showed that the sensitivity of the biosensor was 79% and the specificity was 92%. Therefore, the LSPR biosensor is a valuable tool for serodiagnosis of TB., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Controlled assembly of gold nanorods induced by Na(3)PO(4) leads to a significant amplification of localized surface plasmon resonance (LSPR) signals. The strong affinity between Au and Hg alters the coupled LSPR signals due to the amalgamation of Hg and Au. This allows detection of Hg in aqueous solutions with ultra-high sensitivity and excellent selectivity, without sample pretreatment., (This journal is © The Royal Society of Chemistry 2011)

An enhanced sensitive biosensor has been developed to detect biological targets by tailoring the localized surface plasmon resonance property of core-shell gold nanorods. In this new concept, a shell layer is produced on gold nanorods by generating a layer of chalcogenide on the gold nanorod surface after attachment of the recognition reagent, namely, goat IgG and antigen of schistosomiasis japonica. The bioactivity of these attached biomolecules is retained and the sensitivity of this biosensor is thus enhanced significantly. The plasmonic properties of the gold nanorods attached with the biomolecules can be adjusted and the plasmon resonance wavelength can be red-shifted up to several hundred nanometers in the visible or near infrared (NIR) region, which is extremely important to biosensing applications. This leads to a lager red-shift in the localized surface plasmon resonance absorption compared to the original gold nanorod-based sensor and hence offers greatly enhanced sensitivity in the detection of schistosomiasis japonica. The human serum infected with schistosomiasis japonica diluted to 1:50,000 (volume ratio, serum/buffer solution) can be detected readily. The technique offers enhanced sensitivity and can be easily extended to other sensing applications based on not only immuno-recognition but also other types of specific reactions., (Copyright © 2010 Elsevier B.V. All rights reserved.)

Gold nanorods coated with a multiplex component, namely Au(2)S/AuAgS coated gold nanorods, are produced without precipitation and aggregation among the nanorods. Both the thickness of the shell and size of the core can be readily controlled by this technique allowing one to tune the plasmon resonance of the nanocomposites over a range of several hundred nanometers. These Au(2)S/AuAgS coated gold nanorods exhibit interesting optical properties and are suitable for many biological sensing applications. Functionalization of the Au(2)S/AuAgS coated gold nanorods is achieved by manipulating the affinity between the Au(2)S/AuAgS and thiol compounds. Biomolecules can be covalently attached via the NH(2) bond of the antibodies to the NHS-terminated nanorods. The longitudinal peaks of the Au(2)S/AuAgS coated gold nanorods are extremely sensitive to the refractive index changes induced by target binding, suggesting that they are excellent sensors for target-specific binding events and have the potential to achieve single-molecule sensitivity in microspectroscopy.

We describe the fabrication and characterization of a localized surface plasmon resonance (LSPR) biosensor that utilizes gold nanorods immobilized as the optical transducer which requires the intensity change at a single wavelength to be monitored as a function of receptor-analyte binding at the nanorod surface. In contrary to free gold nanorods suspended in an aqueous solution with high sensitivity to the longitudinal plasmon wavelength to the surrounding environment, the intensity of the longitudinal plasmon band based on immobilized gold nanorods is more sensitive to changes in the surrounding dielectric properties than the change in the longitudinal plasmon wavelength. Quantitative calculation gives a linear equation between the concentration (X) of the test sample and intensity of LPB (Y) as Y=0.0881+12.9502X and 0.1 pM anti-goat can be detected using this IgG probe in this study. This sensor chip made of immobilized gold nanorods is very stable. The immobilized gold nanorods preserved under 4 degrees C for 1 year yield almost the same extinction spectrum as the original nanorods. This study reveals a reliable and sensitive method to measure the intensity of longitudinal plasmon bands based on the highly stable LSPR substrate. Moreover, the performance is comparable to dynamic SPR measurements in immunoassays and can monitor the receptor-analyte reactions in real time.

A novel and sensitive multi-throughput localized surface plasmon resonance (MLSPR) biosensor was developed for the first time. Various gold nanorods with different aspect ratios were used to fabricate the optical sensor. Five kinds of gold nanorods with different aspect ratios were chosen to construct five throughputs of MLSPR. Various LSPR peaks imply that different acceptor-ligand pairs can be detected simultaneously in the wavelength range from 530 to 940nm. The biosensor immobilized on glass slides was applied to label-free detection between acceptor and ligand. The MLSPR-based optical biosensor can be used to detect three antigen-antibody pairs simultaneously. The biosensor proposed herein is easy to fabricate, and its operation procedure is convenient as labeling procedure is unnecessary.

A type of worm-like nanorods was successfully synthesized through conventional gold nanorods reacting with Na2S2O3 or Na2S. The generated worm-like gold nanorods comprise shrunk nanorod cores and enwrapped shells. Therefore, a gold-gold sulfide core-shell structure is formed in the process, distinguishing from their original counterparts. The formation of the gold chalcogenide layers was confirmed by transmission electron microscopy and X-ray photoelectron spectroscopy. Experimental results showed that the thickness of the gold chalcogenide layers is controllable. Since the increase of shell thickness and decrease of gold nanorod core take place simultaneously, it allows one to tune the plasmon resonance of nanorods. Proper adjustment of reaction time, temperature, additives and other experimental conditions will produce worm-like gold nanorods demonstrating desired longitudinal plasmon wavelength (LPW) with narrow size distributions, only limited by properties of starting original gold nanorods. The approach presented herein is capable of selectively changing LPW of the gold nanorods. Additionally, the formed worm-like nanorods possess higher sensitive property in localized surface plasmon resonance than the original nanorods. Their special properties were characterized by spectroscopic methods such as Vis-NIR, fluorescence and resonance light scattering. These features imply that the gold nanorods have potential applications in biomolecular recognition study and biosensor fabrications.

A simple method is presented discriminating proteins at a gold surface by using an emerging technology, surface plasmon resonance (SPR) imaging. As a high throughput method, the protein array of bovine serum albumin (BSA), poly-l-lysine (PL), casein and lactate dehydrogenase (LDG) was fabricated and SPR imaging enables detection from different kinds of proteins immobilized on the sensor surface. These proteins can be discriminated directly by various reflected intensity or changing the incident angular position of light. Denaturation of these immobilized proteins on SPR sensor by interacting with denaturant 6M GdnHCl solution was also performed and obvious changes in reflected intensity were occurred after denaturation. The observation of denaturation of these proteins further supported the fact that different proteins could be discriminated on protein array before denaturation. On the other hand, the procedure of denaturation provided useful information that any change of molecular structure with the progress of denaturation would result in change of SPR signal. Excellent reproducibility with a chip-to-chip for label-free discriminating various proteins was achieved.

A versatile sensitive localized surface plasmon resonance sensor was fabricated for the determination of mercury(II) and cysteine. The determination of mercury(II) was performed by taking advantage of the affinity between core-shell nanostructure and mercury to form a nanocomposite, leading to significant changes of localized surface plasmon resonance properties. The outstanding selectivity and sensitivity of the method provide a unique way to determine mercury(II) to concentrations as low as 5.00 × 10−8 M in aqueous solution. In addition, a strategy of orientation axially (end-to-end) assembly of core-shell gold nanorods at acidic medium was been developed that resulted in coupling of the plasmon band of core-shell gold nanorods, and was the basis of determining cysteine. An ultra-sensitive assay for the determination of cysteine was subsequently developed and levels of cysteine as low as 10−12 M can be determined. Compared with other gold nanorods-based sensors requiring molecular modification, these two approaches are simple in aqueous solution because of the unmodified design. [ABSTRACT FROM AUTHOR]

Abstract: Gold nanorods coated with a multiplex component, namely Au2S/AuAgS coated gold nanorods, are produced without precipitation and aggregation among the nanorods. Both the thickness of the shell and size of the core can be readily controlled by this technique allowing one to tune the plasmon resonance of the nanocomposites over a range of several hundred nanometers. These Au2S/AuAgS coated gold nanorods exhibit interesting optical properties and are suitable for many biological sensing applications. Functionalization of the Au2S/AuAgS coated gold nanorods is achieved by manipulating the affinity between the Au2S/AuAgS and thiol compounds. Biomolecules can be covalently attached via the NH2 bond of the antibodies to the NHS-terminated nanorods. The longitudinal peaks of the Au2S/AuAgS coated gold nanorods are extremely sensitive to the refractive index changes induced by target binding, suggesting that they are excellent sensors for target-specific binding events and have the potential to achieve single-molecule sensitivity in microspectroscopy. [Copyright &y& Elsevier]

Abstract: A multiwavelength surface plasmon resonance (mwSPR) approach has been developed to study the chiral discrimination between d- and l-cystine (Cys). A monolayer of the two enantiomers was separately assembled on a pair of gold films of about 50nm in thickness and their resonance wavelength shifts, Δλ, were measured under a continuous flow of an identical chiral probe solution. Dextran sulfate (DS) was found to be an excellent chiral probe because it has rich chiral centers and is large enough to produce sensitive mwSPR response. The chiral discrimination was investigated either by Δλ max, the maximum resonance wavelength shift in recognition equilibrium, or by recognition kinetics (Δλ vs time). The equilibrium data showed that d-Cys yielded always the smaller Δλ max as compared to l-Cys at pH5.0 or above. This differentiation was enlarged by raising the probe content and became naught at pH <4.5. The kinetic results showed that, as pH increased from 5.0 to 7.5, the non-equilibrium Δλ for d-Cys rose above the level for l-Cys at the first 30s of recognition but came back gradually to its equilibrium position after about 150s, with crossing at 50–150s depending on DS concentration. This phenomenon was thought to be the result of molecular orientation adjustment after DS binding to d-Cys. Both kinetic and thermodynamic mechanisms were thus considered to be deeply involved in the investigated chiral recognition system. [Copyright &y& Elsevier]