Unmodified Gold Nanoparticles Research Articles

A facile and sensitive SERS-based biosensor for colormetric detection of acetamiprid in green tea based on unmodified gold nanoparticles

Surface-enhanced Raman scattering (SERS) has gained a reputation as one of the most sensitive spectroscopic methods for biosensing. However, to design a SERS-based biosensor, almost all currently used methods involve the time-consuming and complicated modification of the metallic nanoparticles, which restricts their wide spread applications. Herein, a facile and sensitive SERS-based aptasensor for colorimetric detection of acetamiprid (AC) was demonstrated. The prepared crystal violet (CV)-aptamer decorated gold nanoparticles (GNPs) tended to aggregate in a solution with high concentrations of salt, and displayed a purple color. In the presence of AC, the specific binding of the target with the aptamer generated conformation changes of aptamer (confirmed by the circular dichroism spectrum), which made the stable GNPs aggregation in the salt solution, thus resulting the SERS signal enhanced. Sequel, the SERS intensity was increased linearly with the concentration of AC ranging from 3.0 × 10−8 to 4.0 × 10−6 M, with a relatively low limit of 1.76 × 10−8 M. The detection ability of AC by this biosensor was also confirmed with different adulterated tea. This approach is not only straightforward in fabrication but also cost-effective in operation, and can be used for diverse bio-molecules detection by changing the aptamer.

Recombinase Polymerase Amplification Combined with Unmodified Gold Nanoparticles for Salmonella Detection in Milk

Salmonella is one of the most common pathogenic bacterium, which causes food spoilage and human diseases. The national standard detection method (GB4789.4) and other fast detection methods for Salmonella cannot satisfy the requirements in the present climate because of their inefficiency, low accuracy, high equipment requirements, or high cost. In this study, we combine isothermal recombinase polymerase amplification (RPA) with unmodified gold nanoparticles (AuNPs) to detect Salmonella in milk. A rapid, effective, visualized, and low-cost RPA-AuNP assay was developed, with a detection limit of 50 CFU for milk samples after enrichment for 6 h or 1 pg for DNA within 15 min at 37 °C using simple water bath equipment. Furthermore, it exhibited no cross-reactions with other pathogens by using highly specific region of invA of Salmonella as the target detection gene. And it may apply to the local food inspection and detection center whose equipment conditions are poor.

A PCR-free voltammetric telomerase activity assay using a substrate primer on a gold electrode and DNA-triggered capture of gold nanoparticles.

The paper describes a voltammetric method for the quantitation of the activity of telomerase extracted from cancer cells. A thiolated single-stranded telomerase substrate primer was firstly immobilized on a gold electrode. In the presence of a mixture of telomerase and deoxynucleotide triphosphates, the primer becomes elongated and contains repetitive nucleotide sequences (TTAGGG)n. After hybridization with blocker DNA, gold nanoparticles are added and captured by the elongated single-stranded DNA. This reduces the charge transfer resistance of the gold electrode. The telomerase activity is then quantified via differential pulse voltammetry, typically at 0.12V (vs. SCE). The method is PCR-free, rapid, and convenient. It was applied to the detection of HeLa cells via the telomerase activity of lysed cells. The detection range was from 500 to 50,000 cells/mL and the detection limit was as low as 500 cells/mL. Graphical abstract A telomerase substrate (TS) primer is immobilized on a gold electrode as the sensing interface to detect the activity of telomerase extracted from cancer cells. Unmodified gold nanoparticles (AuNPs) are utilized which change the electrochemical responses.

DNA colorimetric logic gate in microfluidic chip based on unmodified gold nanoparticles and molecular recognition

Small molecules have been widely developed as drugs, dyes, and research tools. DNA logic system interaction with small molecules as a new analytical method has offered remarkable promise for disease diagnosis and therapy. However, tedious modification process and large sample consumption of traditional DNA logic gates limit the application of this method in bioanalysis. Therefore, developing a simple and less sample consumption platform for DNA logic gates construction is of great importance. Here, we proposed a DNA colorimetric multilevel circuit construction strategy using gold nanoparticles (AuNPs) as an indicator without any modification and labeling step. Two colorimetric logic gates were constructed based on the aggregation of AuNPs mediated by molecular recognition between DNA and protoberberines (palmatine/berberine), including a NIMPLY logic gate and a multi-input NIMPLY + OR logic gate. The logic gate allows the detection of DNA concentrations as low as 0.25 μg/mL by naked eyes within 10 min. More importantly, a microfluidic device was successfully designed to perform the DNA molecular logic gates for reducing reagent consumption and performing precisely and automatically. The working volume of the logic system has been successfully reduced from 0.5 mL in bulk to 22 μL in our designed microfluidic chip, and the DNA solution needed was only 1.1 μL. The method presented here showed great potential in bioanalysis, diagnostics and therapeutics.

Novel and label-free colorimetric detection of radon using AuNPs and lead(II)-induced GR5 DNAzyme-based amplification strategy.

Radioactive radon decays into a stable daughter product, 210Pb, which was used as the detection target to determine the radon radiation dose in a new technique. Pb2+ triggers DNAzyme to cleave a molecular beacon (MB), resulting in the stem-loop structure opening and forming two single DNA strands (ssDNA). The ssDNA binds to unmodified gold nanoparticles and effectively prevents their aggregation in a salt solution. The detached enzyme strands continue to complement the remaining MB to amplify the response signal. The method proposed in this study exhibited a good linear relationship for Pb2+ and radon concentrations in the range of 6.22 × 102-1.02 × 105Bqh/m3 with a detection limit of 186.48Bqh/m3 using an ultraviolet-visible spectrometer. In practical applications, this sensitive method can avoid radioactive damage in field testing, and the detection limit meets the national standard in China. Importantly, this simple, highly sensitive strategy uses simple equipment and has a strong anti-interference ability. Graphical abstract.

Gold nanoparticles dispersion stability under dynamic coating conditions in capillary zone electrophoresis

Capillary zone electrophoresis (CZE) of unmodified gold nanoparticles (Au NPs) was investigated in terms of dispersion stability in a presence of buffering counter-ions in background electrolyte (BGE). Capillary length, migration time and electric field strength were identified among factors influencing particles CZE. Moreover, BGE electrolysis was found to significantly affect analyses repeatability. The adsorption of NPs to capillary wall was recognized as the main problem. It was shown that this inconvenience can be overcome by the application of relatively big counter-ions. According to this observation, steric stabilization of NPs suspension by BGE components during CZE was hypothesized. In result, repeatable CZE of bare Au NPs under dynamic coating conditions was shown.

Highly Sensitive Colorimetric Biosensor for Staphylococcal Enterotoxin B by a Label-Free Aptamer and Gold Nanoparticles.

A simple, sensitive and selective colorimetric biosensor for the detection of Staphylococcal enterotoxin B (SEB) was developed using SEB-binding aptamer (SEB2) as recognition element and unmodified gold nanoparticles (AuNPs) as colorimetric probes. The assay is based on color change from red to purple due to conformational change of aptamer in the presence of SEB, and the phenomenon of salt-induced AuNPs aggregation which could be monitored by naked eye or UV–vis spectrometer. Results showed that the AuNPs can effectively differentiate the SEB induced conformational change of the aptamer in the presence of a given high salt concentration. A linear response in the range of 50 μg/mL to 0.5 ng/mL of SEB concentration was obtained. The assay was highly specific to SEB as compared to other related toxins. The limit of detection (LOD) of SEB achieved within few minutes was 50 ng/mL visually and spectrometric method improved it to 0.5 ng/mL. Robustness of the assay was tested in artificially spiked milk samples and cross-checked using in house developed sandwich ELISA (IgY as capturing and SEB specific monoclonal as revealing antibody) and PCR. This colorimetric assay could be a suitable alternative over existing methods during biological emergencies due to its simplicity, sensitive and cost effectiveness.

A colorimetric platform for sensitively differentiating telomere DNA with different lengths, monitoring G-quadruplex and dsDNA based on silver nanoclusters and unmodified gold nanoparticles

Human telomere DNA plays a vital role in genome integrity control and carcinogenesis as an indication for extensive cell proliferation. Herein, silver nanoclusters (Ag NCs) templated by polymer and unmodified gold nanoparticles (Au NPs) are designed as a new colorimetric platform for sensitively differentiating telomere DNA with different lengths, monitoring G-quadruplex and dsDNA. Ag NCs can produce the aggregation of Au NPs, so the color of Au NPs changes to blue and the absorption peak moves to 700nm. While the telomere DNA can protect Au NPs from aggregation, the color turns to red again and the absorption band blue shift. Benefiting from the obvious color change, we can differentiate the length of telomere DNA by naked eyes. As the length of telomere DNA is longer, the variation of color becomes more noticeable. The detection limits of telomere DNA containing 10, 22, 40, 64 bases are estimated to be 1.41, 1.21, 0.23 and 0.22nM, respectively. On the other hand, when telomere DNA forms G-quadruplex in the presence of K+, or dsDNA with complementary sequence, both G-quadruplex and dsDNA can protect Au NPs better than the unfolded telomere DNA. Hence, a new colorimetric platform for monitoring structure conversion of DNA is established by Ag NCs-Au NPs system, and to prove this type of application, a selective K+ sensor is developed.

Colorimetric Aptasensor for Detection of Malachite Green in Fish Sample Based on RNA and Gold Nanoparticles

A facile colorimetric aptasensor based on unmodified gold nanoparticles (AuNPs) for rapid, highly sensitive and selective detection of malachite green (MG), one of triphenylmethane dyes and antibiotics, was successfully developed. Malachite green RNA aptamer having the binding ability with high affinity and specificity would be the ideal recognition receptor for MG. RNA aptamer can adsorb on the AuNPs and protect AuNPs against salt-induced aggregation. When malachite green were added in a solution, aggregation of AuNPs was specifically induced by desorption of aptamer from the surface of gold nanoparticles as the formation of aptamer-target complex. Therefore, the salt could trigger AuNP aggregate and the solution color changed from red to blue. The solution colors and absorbance were related with the concentrations of MG, and a well linear relationship in the wide range was obtained. The detection limit of MG was down to 15.95 nM. This colorimetric method was better than other traditional methods in terms of its reduced detection time, simple signal generation, high selectivity, lower detection limit, and observation with the naked eye. The proposed one-step, label-free method was successfully used to determine MG in actual fish samples. The high recoveries of MG in fish sample detection were satisfied.

Colorimetric sensing of mercury (II) ion based on anti-aggregation of gold nanoparticles in the presence of hexadecyl trimethyl ammonium bromide

A new specific and sensitive colorimetric sensor based on anti-aggregation of unmodified gold nanoparticles (AuNPs) for mercury ion detection was studied by forming Au-Hg alloys deposited onto the surface of AuNPs. In the protocol, hexadecyl trimethyl ammonium bromide (CTAB) could cause the aggregation of AuNPs and induced the color change from red to blue due to the strong electrostatic attraction between CTAB and citrate ion capped gold nanoparticles. In the presence of Hg2+, citrate ion capped AuNPs reduced Hg2+ to Hg and then formed Hg-Au alloys, which could inhibit the aggregation of AuNPs caused by CTAB to some extent. Based on these findings, Hg2+ was detected by a blue-to-red color change of AuNPs solution containing CTAB. Also, the limit of detection (LOD) was 11.9 nM by UV–vis spectroscopy, which was lower than the guideline concentration of Hg2+ (30 nM) in drinking water set by the World Health Organization (WHO). And the results showed the absorbance ratios A650/A520 had a good linear correlation with the Hg2+ concentration from 0 to 680 nM, which could be used for the quantitative detection of Hg2+. This method was successfully used to detect Hg2+ in tap water sample.

Colorimetric aptasensors for determination of tobramycin in milk and chicken eggs based on DNA and gold nanoparticles

Colorimetric aptasensors were designed for detection of tobramycin (TOB) based on unmodified gold nanoparticles (AuNPs) and single-strand DNA (ssDNA). In the absence of TOB, the DNA aptamer was coated on the surface of AuNPs to keep it against salt-induced aggregation. In the presence of TOB, aptamer will bind with TOB and detach from the surface of AuNPs because of higher affinities between aptamer and TOB. Then less protection of DNA may result in the aggregation of AuNPs by salt and an apparent color change from red to purple-blue. The developed aptasensors showed a high selectivity and sensitivity for TOB detection. The linearity range and the detection limit were 40–200 nM and 23.3 nM respectively. The validity of the procedure and applicability of aptasensors were successfully used to detect TOB in milk and chicken eggs, and the results were excellent in accord with the values obtained by spectrofluorimetric detection.

Colorimetric detection of protein via the terminal protection of small-molecule-linked DNA and unmodified gold nanoparticles.

A novel colorimetric strategy for protein detection was developed based on unmodified gold nanoparticles (AuNPs) and terminal protection from a target protein. A hairpin-structured DNA probe with a biotin modification at the 3′ terminus combined with streptavidin (SA) by the high affinity between biotin and SA and resisted degradation from exonucleases III (Exo III), which selectively digested double-stranded DNA from the 3′-terminus. The remaining hairpin DNA lost the capacity to protect AuNPs from salt-induced aggregation, resulting in a color change of AuNPs from red to blue. In the absence of SA, Exo III degraded the hairpin DNA into single-stranded DNA, which adsorbed on the surfaces of AuNPs and prevented aggregation, keeping AuNPs with a red color. The state of AuNP aggregation can be discriminated by colorimetry and also can be measured by UV-vis spectroscopy. Our proposed method provided great selectivity and high sensitivity with a detection limit of 0.24 pmol for SA detection. Moreover, the assay avoided modification, enzymatic amplification and special equipment, and also offered the advantages of being simple, cost-effective, and sensitive. This novel strategy holds great promise for the detection of other proteins by small molecule interactions with proteins.

Towards an Effective Management on the Teaching and Learning of Accounting in Simple and Rapid Colorimetric Bio-sensing of Alpha-fetoprotein Using Aptamer and Unmodified Gold Nanoparticles

A simple and rapid colorimetric method for determination of alpha-fetoprotein (AFP) has been developed here using specific aptamers and free gold nanoparticles (AuNPs). In the absence of AFP, the free aptamers prevent aggregation of AuNPs in a high salt environment, which cause the mixed solution remain red. Conversely, when there are existing AFP in colorimetric system, the aptamers is consumed to decrease, forming aptamer-AFP complex. AuNPs were aggregated due to losting the protection from aptamers in the high salt solution. The color of the solution turns to blue at this time. Subsequently, a color change of red-to-blue can be observed by the naked eye with the increasing of AFP. The linear response range for AFP was 10 to 2000 ng/ml and the detection limit was 5 ng/ml. This colorimetric biosenser does not require any modification, and its composition is cheap and easy to obtain. In addition, this proposed colorimetric method is also used in simulative hepatocellular carcinoma (HCC) serum samples and showed good feasibility, holding great potential for preliminary screening of serum of HCC in the future.

Ultrasensitive point-of-care testing of arsenic based on a catalytic reaction of unmodified gold nanoparticles

Ultrasensitive arsenic detection based on inhibition of a catalytic reaction between Rhodamine B and sodium borohydride.

Highly selective and sensitive determination of dopamine in biological samples via tuning the particle size of label-free gold nanoparticles

Herein, a rapid, sensitive and selective approach for the colorimetric detection of dopamine (DA) was developed utilizing unmodified gold nanoparticles (AuNPs). This assay relied upon the size-dependent aggregation behavior of DA and three other structurally similar catecholamines (CAs), offering highly specific and accurate detection of DA. By means of this study, we attempted to overcome the tedious procedures of surface premodifications and achieve selectivity through tuning the particle size of AuNPs. DA could induce the aggregation of the AuNPs via hydrogen-bonding interactions, resulting in a color change from pink to blue which can be monitored by spectrophotometry or even the naked-eye. The proposed colorimetric probe works over the 0.1 to 4μM DA concentration range, with a lower detection limit (LOD) of 22nM, which is much lower than the therapeutic lowest abnormal concentrations of DA in urine (0.57μM) and blood (16μM) samples. Furthermore, the selectivity and potential applicability of the developed method in spiked actual biological (human plasma and urine) specimens were investigated, suggesting that the present assay could satisfy the requirements for clinical diagnostics and biosensors.

A simple and sensitive sensor for silver ions based on unmodified gold nanoparticles by using dynamic light scattering techniques

A simple and sensitive assay for Ag+ was developed with unmodified gold nanoparticles (AuNPs) by using dynamic light scattering techniques. Ag+ could induce the oligonucleotide (5′-ATC ACT ATA TCA TAT ACT CAT-3′) to change from a single-stranded structure to a double-stranded structure and desorb from the surface of AuNPs, which triggered the aggregation of AuNPs in the salt solution. The average hydrodynamic diameter of aggregated AuNPs could be detected by using dynamic light scattering techniques. Under the optimum conditions, the average hydrodynamic diameter of AuNPs is proportional to the concentration of Ag+ within the range of 13.3–100.0 nmol/L, with a detection limit of 3.2 nmol/L. The method is easy to operate and has low sample consumption, high sensitivity and selectivity.

Colorimetric detection of DNA by using target catalyzed DNA nanostructure assembly and unmodified gold nanoparticles

The authors describe a strategy for colorimetric detection of DNA. It is making use of a target catalyzed DNA nanostructure assembly and gold nanoparticles. The assay comprises the following steps: (a) A programmed DNA nanostructure is assembled from three auxiliary hairpin structure DNAs and the single stranded DNA (ssDNA; the target/analyte); (b) in the presence of target DNA, these three hairpin DNAs are opened, thereby activating a catalytic self-assembly process via a target assisted toe-hold strand displacement reaction; (c) The formed DNA nanostructures are mixed with gold nanoparticles. As the DNA nanostructure is less stabilized without ssDNA sticky ends, it cannot prevent the gold nanoparticles (AuNPs) to undergo salt-induced aggregation which is accompanied by a color change from purple to blue; (d) The color change of the colloid solution can be read out with bare eyes or instrumentally. The detection limit by using UV–vis spectrometry is 0.6 pM of target DNA. This is comparable to previously AuNP-based methods. Thus, this assay provides free modification detection based on DNA nanostructure without sophisticated procedures. Conceivably, the method can be applied to numerous other DNA targets.

Colorimetric Detection of Unamplified Rift Valley Fever Virus Genetic Material Using Unmodified Gold Nanoparticles.

Rift Valley fever virus (RVFV) is considered an enzootic virus in Africa. RVFV has caused several outbreaks in Egypt, sub-Saharan Africa and the Arabian Peninsula and is responsible for high mortality in ruminants and haemorrhagic fever in severe human cases. Although there are several molecular and serological diagnostic techniques used to detect this arthropod-borne virus with high sensitivity and efficiency, there is a need for a fast and reliable field screening test for rapid outbreak recording and containment. In this study, we developed a prototype point-of-care diagnostic test specific for RVFV detection using unmodified gold nanoparticles (AuNPs) that change colour in the presence of RVFV RNA, resulting in a simple but sensitive assay. The nanogold assay provides qualitative results showing the presence of the RVFV RNA in different sample types. The assay showed high accuracy and specificity, with a detection limit of 10 RNA copies/reaction, comparable with quantitative reverse transcription polymerase chain reaction. The assay result could be determined within 30min with no need for specific detection instruments. To our knowledge, this is the first field test prototype to directly detect the RNA of RVFV without amplification using AuNPs.

Development of a Paper-Based Plasmonic Test Strip for Visual Detection of Methiocarb Insecticide

This paper describes a simple and low-cost test strip for on-site monitoring of methiocarb insecticide. Hydrophilic filter paper soaked in agarose solution was bounded by hydrophobic solid wax and then was coated with unmodified gold nanoparticles (AuNPs). AuNPs aggregation caused by methiocarb served as colorimetric response. We demonstrated detection capability of methiocarb both in solution- and substrate-based sensor. A good linear relationship was obtained between the colorimetric response and the concentration of methiocarb ranging from 20 to 80 ng mL $^{-1}$ with a limit of detection of 5 ng mL $^{-1}$ . Excellent selectivity toward methiocarb was observed among various pesticides and cationic and anionic ions. Furthermore, the proposed assay could successfully detect methiocarb in paddy and tap water with satisfactory results. It would be of interest for use as rapid, portable, and technically simple test strip in water quality monitoring.

Diagnosis of Tuberculosis Using Colorimetric Gold Nanoparticles on a Paper-Based Analytical Device.

We have developed a colorimetric sensing strategy employing gold nanoparticles and a paper-based analytical platform for the diagnosis of tuberculosis (TB). By utilizing the surface plasmon resonance effect, we were able to monitor changes in the color of a gold nanoparticle colloid based on the effects of single-stranded DNA probe molecules hybridizing with targeted double-stranded TB DNA. The hybridization event changes the surface charge density of the nanoparticles, causing them to aggregate to various degrees, which modifies the color of the solution in a manner that can be readily measured to determine the concentration of the targeted DNA analyte. In order to adapt this TB diagnosis method to resource-limited settings, we extended this label-free oligonucleotide and unmodified gold nanoparticle solution-based technique to a paper-based system that can be measured using a smartphone to obtain rapid parallel colorimetric results with low reagent consumption and without the need for sophisticated analytical equipment. In this study, we investigated various assay conditions, including the denaturing temperature and time, different oligonucleotide probe sequences, as well as the ratio of single stranded probe and double stranded target DNA. After optimizing these variables, we were able to achieve a detection limit of 1.95 × 10-2 ng/mL for TB DNA. Furthermore, multiple tests could be performed simultaneously with a 60 min turnaround time.