A highly selective and sensitive on-off sensor for silver ions and cysteine by light scattering technique of DNA-functionalized gold nanoparticles

DNA-functionalized gold nanoparticles are shown to act as a light-scattering switch. Ag(+) ion turns on the switch through the DNA-Au NPs conjugates based on the formation of cytosine-Ag(+)-cytosine base pairs, whereas cysteine turns off the light-scattering signal because it competitively binds to Ag(+).     

Ultrasensitive detection of lead(II) with DNAzyme and gold nanoparticles probes by using a dynamic light scattering technique

A dynamic light scattering sensor for Pb(2+) was constructed with oligonucleotide-modified gold nanoparticles based upon its cleavage property for DNAzyme.     

A one-step highly sensitive method for DNA detection using dynamic light scattering

A one-step homogeneous DNA detection method with high sensitivity was developed using gold nanoparticles (AuNPs) coupled with dynamic light scattering (DLS) measurement. Citrate-protected AuNPs with a diameter of 30 nm were first functionalized with two sets of single-stranded DNA probes and then used as optical probes for DNA detection. In the presence of target DNA, the hybridization between target DNA and the two nanoparticle probes caused the formation of nanoparticle dimers, trimers, and oligomers. As a result, the nanoparticle aggregation increased the average diameter of the whole nanoparticle population, which can be monitored simply by DLS measurement. A quantitative correlation can be established between the average diameter of the nanoparticles and the target DNA concentration. This DLS-based assay is extremely easy to conduct and requires no additional separation and amplification steps. The detection limit is around 1 pM, which is 4 orders of magnitude better than that of light-absorption-based methods. Single base pair mismatched DNAs can be readily discriminated from perfectly matched target DNAs using this assay.     

One-step assay for detecting influenza virus using dynamic light scattering and gold nanoparticles

Herein we detail the development of a simple, rapid, and sensitive method for quantitative detection of influenza A virus using dynamic light scattering (DLS) and gold nanoparticle (AuNP) labels. Influenza-specific antibodies are conjugated to AuNPs, and aggregation of the AuNP probes is induced upon addition of the target virus. DLS is used to measure the extent of aggregation and the mean hydrodynamic diameter is correlated to virus concentration. The effects of nanoparticle concentration and size on the analytical performance of the assay were systematically investigated. It was determined that decreasing the AuNP probe concentration improves the detection limit while the effect of changing the AuNP size is minimal. Optimization of the assay provided a detection limit of <100 TCID(50)/mL which is 1-2 orders of magnitude improved over commercial diagnostic kits without increasing the assay time or complexity. Additionally, this assay was demonstrated to perform equivalently for influenza virus prepared in different biological matrices.     

Glucose detection at attomole levels using dynamic light scattering and gold nanoparticles

Glucose is directly related to brain activity and to diabetes.Therefore,developing a rapid and sensitive method for glucose detection is essential.Here,label-free glucose detection at attomole levels was realized by detecting the average diameter change of gold nanoparticles(AuNPs)utilizing dynamic light scattering(DLS).Single-strand DNA(ssDNA)adsorbed into the AuNPs’surfaces and prevented them from aggregating in solution that contained NaCl.However,ssDNA cleaved onto ssDNA fragments upon addition of glucose,and these fragments could not adsorb onto the AuNPs’surfaces.Therefore,in high-salt solution,AuNPs would aggregate and their average diameter would increase.Based on monitoring the average diameter of AuNPs with DLS,glucose could be detected in the range from 15 pmol/L to 2.0 nmol/L,with a detection limit of 8.3 pmol/L.Satisfactory results were also obtained when the proposed method was applied in human serum glucose detection.     

A DNA biosensor based on resonance light scattering using unmodified gold bipyramids

We report on a novel biosensor for determining sequence-specific DNA. It is based on resonance light scattering (RLS) caused by the aggregation of gold bipyramids. These display localized surface plasmon resonance and can be used as a bioprobe. The absorption spectra and the transmission electron micrographs provide visual evidence of the aggregation of the gold bipyramids in the presence of DNA. The RLS intensity of the gold bipyramids increases with the concentration of the target DNA. The method was successfully applied to the determination of a 30-mer single-stranded oligonucleotide and works over the 0.1–10?nM concentration range.

Colorimetric Cu2+ detection with a ligation DNAzyme and nanoparticles

Using a Cu(2+)-dependent DNA ligation DNAzyme, a colorimetric sensor for Cu2+ has been developed based on directed assembly of DNA-functionalized gold nanoparticles by the ligation product, and such ligation DNAzyme-based sensors are intrinsically more sensitive than cleavage DNAzyme systems due to the lack of background.     

A highly sensitive assay for protein with dibromochloro-arsenazo-Al(3+) using resonance light scattering technique and its application

A simple, sensitive and selective method has been developed for the determination of protein using resonance light scattering (RLS) technique. The method is based on the interaction of protein and arsenazo-DBC-Al(3+) in the pH range of 5.0-7.0, which causes a substantial enhancement of the resonance scattering signal of arsenazo-DBC-Al(3+) in the wavelength range of 300-550 nm with the maximum RLS platform at 405-420 nm. With this method, 2.50-50.00 mug ml(-1) of bovine serum albumin (BSA) and 2.50-60.00 mug ml(-1) of human serum albumin (HSA) can be determined, and the detection limits, calculated three times the standard deviation (S.D.) of six blank measurements, for BSA and HSA were 123.4 and 89.6 ng ml(-1), respectively. Moreover, the method is free from interference from many amino acids and metal ions. The method, with high sensitivity, selectivity and reproducibility, was satisfactorily applied to the determination of total protein in human serum samples. Mechanism studies indicated that arsenazo-DBC-Al(3+) could bind to BSA depending mainly on electrostatic forces, which results in enhanced RLS in the arsenazo-DBC-Al(3+)-protein system.     

A sensitive resonance light scattering spectrometry of trace Hg with sulfur ion modified gold nanoparticles

A new resonance light scattering (RLS) spectrometric method for mercury ions (Hg²⁺) in aqueous solutions with sulfur ion (S²⁻) modified gold nanoparticles (Au-NPs-S) has been developed in this contribution. It was found that S²⁻ at the surface of Au-NPs resulting from the surface modification can interact with Hg²⁺ to form very stable S-Hg-S bonds when Hg²⁺ concentration is lower than that of S²⁻, resulting in the aggregation of Au-NPs-S and causing enhanced RLS signals. The enhanced RLS intensities (ΔI_RLS) characterized at 392 nm were found to be proportional to the concentration of Hg²⁺ in the range of 0.025-0.25 μmol L⁻¹ with a detection limit (3σ) of 0.013 μmol L⁻¹. Our results showed that this approach has excellent selectivity for Hg²⁺ over other substances in aqueous solutions.     

Influence of particle size on the SARS-CoV-2 spike protein detection using IgG-capped gold nanoparticles and dynamic light scattering

Due to the unprecedented and ongoing nature of the coronavirus outbreak, the development of rapid immunoassays to detect severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and its highly contagious variants is an important and challenging task. Here, we report the development of polyclonal antibody-functionalized spherical gold nanoparticle biosensors as well as the influence of the nanoparticle sizes on the immunoassay response to detect the SARS-CoV-2 spike protein by dynamic light scattering. By monitoring the increment in the hydrodynamic diameter (ΔD_H) by dynamic light scattering measurements in the antigen–antibody interaction, SARS-CoV-2 S-protein can be detected in only 5 min. The larger the nanoparticles, the larger ΔD_H in the presence of spike protein. From adsorption isotherm, the calculated binding constant (K_D) was 83 nM and the estimated limit of detection was 13 ng/mL (30 pM). The biosensor was stable up to 90 days at 4 °C. Therefore, the biosensor developed in this work could be potentially applied as a fast and sensible immunoassay to detect SARS-CoV-2 infection in patient samples.     

Assembly of DNA-functionalized gold nanoparticles studied by UV/Vis-spectroscopy and dynamic light scattering

The DNA mediated assembly of complementary DNA-functionalized gold nanoparticles (DNA-AuNP) was investigated by means of UV/Vis-spectroscopy and Dynamic Light Scattering (DLS). The melting temperature of the aggregates was determined to be T(m) = 31 degrees C. Characterization of the assembly at 20 degrees C, 25 degrees C and 30 degrees C showed a decrease of the initial assembly growth rate with increasing temperature. The correlation of the wavelengths at the absorbance maxima lambda(max) and the hydrodynamic radii R(h) of the AuNP assemblies proved the dependence of the optical properties on the assembly size while at higher assembly temperature (30 degrees C) a larger redshift of lambda(max) with increasing R(h) was observed than at lower temperatures. This tendency might give information about the dependence of the internal structure of the DNA-AuNP assemblies on assembly temperature. It is assumed that at higher temperatures more compact assemblies are built than at lower temperatures of 20 degrees C and 25 degrees C. To the best of our knowledge, this is the first systematic time-resolved in situ investigation of DNA-mediated AuNP assembly by UV/Vis-spectroscopy and DLS.     

Rapid and sensitive detection of cholera toxin using gold nanoparticle-based simple colorimetric and dynamic light scattering assay

Herein, a rapid and simple gold nanoparticle based colorimetric and dynamic light scattering (DLS) assay for the sensitive detection of cholera toxin has been developed. The developed assay is based on the distance dependent properties of gold nanoparticles which cause aggregation of antibody-conjugated gold nanoparticles in the presence of cholera toxin resulting discernible color change. This aggregation induced color change caused a red shift in the plasmon band of nanoparticles which was measured by UV–Vis spectroscopy. In addition, we employed DLS assay to monitor the extent of aggregation in the presence of different concentration of cholera toxin. Our assay can visually detect as low as 10 nM of cholera toxin which is lower than the previously reported colorimetric methods. The reported assay is very fast and showed an excellent specificity against other diarrhetic toxins. Moreover, we have demonstrated the feasibility of our method for cholera toxin detection in local lake water.     

Hydrogen-bonding recognition-induced aggregation of gold nanoparticles for the determination of the migration of melamine monomers using dynamic light scattering

The migration of melamine monomers from food contact materials has aroused particular attention since the 2008 melamine-tainted milk scandal in China. However, the determination of melamine monomer’s migratory quantity (MMMQ) has remained an open question because of the complex sample pretreatment and the low sensitivity. Based on the hydrogen bonding interaction between DNA thymine and melamine, this paper described a simple and rapid method focusing on the measurement of MMMQ from melamine tableware by gold nanoparticles (GNPs) and dynamic light scattering (DLS). With the presence of probe DNA (p-DNA), the GNPs were stable in NaCl solution (0.06 M), whereas they became aggregated when the p-DNA hybridized with melamine. The change in the hydrodynamic diameter of GNPs could be detected by DLS technology. Under the optimal conditions, the average diameter increased linearly with the concentration of melamine over the range from 5.0 to 320.0 μg L⁻¹, and showed a detection limit of 2.0 μg  L⁻¹ (3σ/slope). The MMMQ was investigated within a range from 6.00 × 10⁻⁴ to 2.58 × 10⁻¹ mg dm⁻² (n ≥ 3) in four different food simulants at different temperatures and time points. The results suggest that the DLS method has great potential in the analysis of the migration of melamine monomers.     

Mercuric ions induced aggregation of gold nanoparticles as investigated by localized surface plasmon resonance light scattering and dynamic light scattering techniques

With the development of nanosciences, both localized surface plasmon resonance light scattering (LSPR-LS) and dynamic light scattering (DLS) techniques have been widely used for quantitative purposes with high sensitivity. In this contribution, we make a comparison of the two light scattering techniques by employing gold nanoparticles (AuNPs) aggregation induced by mercuric ions. It was found that citrate-stabilized AuNPs got aggregated in aqueous medium in the presence of mercuric ions through a chelation process, resulting in greatly enhanced LSPR-LS signals and increased hydrodynamic diameter. The enhanced LSPR-LS intensity ( I) is proportional to the concentration of mercuric ions in the range of 0.4-2.5 M following the linear regression equation of I = 84.7+516.4c, with the correlation coefficient of 0.983 (n = 6) and the limit of determination (3 ) about 0.10 M. On the other hand, the increased hydrodynamic diameter can be identified by the DLS signals only with a concentration of Hg 2+ in the range of 1.0-2.5 M, and a linear relationship between the average hydrodynamic diameters of the resulted aggregates and the concentration of Hg 2+ can be expressed as d = 6.16 + 45.9c with the correlation coefficient of 0.994. In such case, LSPR-LS signals were further applied to the selective determination of mercuric ions in lake water samples with high sensitivity and simple operation.     

Sensitive and selective detection of glutathione based on resonance light scattering using sensitive gold nanoparticles as colorimetric probes

In this paper, we reported the development of a highly sensitive and selective resonance light scattering (RLS) technique for glutathione using gold nanoparticle probes. The assay relies upon the distance-dependent optical properties of gold nanoparticles, the self-assembly of glutathione on gold nanoparticles, and the interaction of a 2 : 1 glutathione-Cu(2+) complex. In the presence of Cu(2+), glutathione could rapidly induce the aggregation of gold nanoparticles, thereby resulting in greatly enhanced RLS intensity and red-to-blue (or purple) color change. The concentration of glutathione can be determined by the naked eye or a fluorescence spectrometer. Under the optical conditions, the detection of glutathione can be finished within 20 min, and the detection limit of 10 nM can be reached. The concentration range of the probe is 40-280 nM. The proposed method holds a specific selectivity toward glutathione and it is applied to the detection of glutathione in human serum with satisfactory results. In addition, the assay shows great potential application for disease-associated biomarkers, and it will meet the great demand for amino acid determination in fields such as food processing, biochemistry, pharmaceutical, and clinical analysis.     

Metal-chelating nanoparticles as selective fluorescent sensor for Cu2+

A fluorescent sensor for Cu(2+) at the nanomolar level in water has been designed by associating a BODIPY fluorophore and a selective ligand (cyclam) in ultrafine polymer nanoparticles.     

A one-step homogeneous immunoassay for cancer biomarker detection using gold nanoparticle probes coupled with dynamic light scattering

A one-step homogeneous immunoassay for the detection of a prostate cancer biomarker, free-PSA (prostate specific antigen), was developed using gold nanoparticle probes coupled with dynamic light scattering (DLS) measurements. A spherical gold nanoparticle with a core diameter around 37 nm and a gold nanorod with a dimension of 40 by 10 nm were first conjugated with two different primary anti-PSA antibodies and then used as optical probes for the immunoassay. In the presence of antigen f-PSA in solution, the nanoparticles and nanorods aggregate together into pairs and oligomers through the formation of a sandwich type antibody-antigen-antibody linkage. The relative ratio of nanoparticle-nanorod pairs and oligomers versus individual nanoparticles was quantitatively monitored by DLS measurement. A correlation can be established between this relative ratio and the amount of antigen in solution. The light scattering intensity of nanoparticles and nanoparticle oligomers is several orders of magnitude higher than proteins and other typical molecules, making it possible to detect nanoparticle probes in the low picomolar concentration range. f-PSA in the concentration range from 0.1 to 10 ng/mL was detected by this one-step and washing-free homogeneous immunoassay.     

Highly sensitive and selective fluorescent sensor for Zn2+/Cu2+ and new approach for sensing Cu2+ by central metal displacement

An "off-on" Zn(2+) and "on-off" Cu(2+) fluorescent chemosensor C was designed and synthesized. The binding of C and Zn(2+)/Cu(2+) is chemically reversible by the addition of EDTA disodium solution; moreover, the fluorescence emission signal of ZnC decreased with the addition of Cu(2+), demonstrating that ZnC could detect Cu(2+)via metal displacement.