Surface-enhanced Raman Scattering Aptasensor Research Articles

Assembly of stabilized dendritic magnetic ferric-silver nanocomposite with gold nanoparticles for sensitive detection of ochratoxin A using SERS aptasensor

Ochratoxin A (OTA) contamination poses a significant global threat to food security, necessitating the development of rapid and effective detection methods. A dendritic magnetic silver nanocomposite (Fe3O4@SiO2@Ag) tagged with aptamers acted as surface-enhanced Raman scattering (SERS) substrates and capture probes. Further, gold nanoparticles (AuNPs) were functionalized with cDNA and utilized as Raman-enhanced probes (cDNA-AuNPs). The SERS aptasensor which was constructed by the assembly of Apt-Fe3O4@SiO2@Ag and cDNA-AuNPs attained the accuracy quantitative and extremely sensitive detection of OTA. An inverse relationship between the concentration of OTA standard solution and Raman intensity of the characteristic peak at 1080 cm−1 was established in the range of 0.01–5 ng/mL, with an LOD of 0.0074 ng/mL. Furthermore, for positive corn samples, the coincidence rate between the established SERS aptamer sensor and HPLC was in the range of 92.67–121.10%, demonstrating tremendous promise for future practical application through other crops.

Trace Detection of E. coli O157:H7 Cells by an Au Nanoparticle-Based SERS Aptasensor

Drinking polluted water can cause deadly diseases, and clean water is becoming increasingly scarce in the environment. Various pathogens in water will affect environmental safety and human health, so it is necessary to detect pathogens with sensitivity, specificity, simplicity, and celerity. Here, we designed a surface-enhanced Raman scattering (SERS) adaptive sensor based on rolling cycle amplification (RCA), in which the introduced Au nanoparticle-based SERS aptasensor could transform the concentration signal of Escherichia coli into a Raman signal, realizing the sensitive analysis of E. coli O157:H7 (E. coli O157:H7). In this strategy, the magnetic beads were modified with double-stranded DNA (dsDNA) to recognize E. coli and initiate RCA. In the presence of E. coli, one strand of dsDNA will recognize it and unchained from dsDNA and the other strand of dsDNA will act as a trigger for RCA. Then, the RCA reaction was initiated. A large number of SERS probes can be attached to RCA products to achieve a strong Raman signal. Under the optimal conditions, we obtained a low limit of detection (LOD = 0.3 CFU/mL) and a wide detection range (102–107 CFU/mL). Also, this SERS aptasensor can complete the detection within 45 min. It can be concluded that this SERS aptasensor has wide application prospects in food safety inspections, environmental monitoring, and clinical diagnosis, as it can provide a fast, sensitive, and one-pot platform for bacterial detection.

Simultaneous detection of trace Hg2+ and Ag+ by SERS aptasensor based on a novel cascade amplification in environmental water

Mercury ions and silver ions will be doped in environment during the entire process of water circulation, which is harmful to ecological balance and human body. Surface Enhanced Raman Scattering (SERS) acts as an effective method in detecting heavy metal ions, due to its easy processing, rapid detection, and fingerprintidentification. At present, it is still a challenge to simultaneously detect multiple heavy metal ions based on SERS sensor. Herein, we developed a new SERS aptasensor, applying cascade nucleic acid amplification strategy to detect Hg2+ and Ag+, which greatly improved the sensitivity. Meanwhile, the use of aptamers can transform the concentrations of Hg2+ and Ag+ into DNA signal. And thymine-Hg2+-thymine and cytosine-Ag+-cytosine pairs were formed to simultaneously identify Hg2+ and Ag+. Multiple analytical strategy of this SERS aptasensor can not only avoid the inconvenience caused by different techniques or experiment conditions, but also reduce cost, time, and difficulty. In consequence, we obtained a lower detection limitation (LOD Hg2+=4.40 aM, LOD Ag+=9.97 aM) in the linear range of 0.2–125 fM. The results demonstrate that this SERS aptasensor is capable of being widely applied to simultaneously detect multiple heavy metal ions or other toxic substance in environmental water.

Hydrophobic Plasmonic Nanoacorn Array for a Label-Free and Uniform SERS-Based Biomolecular Assay.

A surface-enhanced Raman scattering (SERS) aptasensor based on a hydrophobic assembled nanoacorn (HANA) was developed with improved reproducibility and reduced nonspecific binding effect. In the fabrication process, a hexagonal-packed gold film over nanosphere (AuFON) arrays was first obtained and used as a hydrophobic plasmonic substrate. Then, a uniform sub-3 nm molecular spacer array (containing Raman reporters) was prepared by patterning nanometric hydrophilic ultrathin patches onto the hydrophobic AuFON, in which the hydrophilic thin layer is composed of polymers and aptamers. During the sensing process, the HANA aptasensor smartly impedes the adsorption of SERS probes as Au@Ag nanocubes (Au@Ag NCs) in the absence of targets. In the presence of targets, the displacement of aptamers occurs due to the specific interaction between the targets and the aptamers, and the Au@Ag NCs can be assembled onto the hydrophilic patches on AuFON through electrostatic interactions with polymers. Thus, SERS signals of reporter molecules inside the spacer can be dramatically enhanced due to the formation of a nanoparticle-on-mirror (NPoM) array. In such a SERS aptasensor, the well-ordered distribution of SERS probes ensures excellent repeatability, while the precise subnanometer junctions guarantee high sensitivity. More importantly, since the hydrophobic surface can greatly reduce nonspecific adsorption, the tedious process of nonspecific blocking that is employed in traditional biosensors is no longer needed. Using such a SERS HANA platform, human epidermal growth factor receptor 2 (HER2) and three exosomal proteins were analyzed with high sensitivity and good reproducibility (RSD < 7%) in whole-blood samples.

Indirect surface-enhanced Raman scattering assay of insulin-like growth factor 2 receptor protein by combining the aptamer modified gold substrate and silver nanoprobes.

An indirect aptamer-based SERS assay for insulin-like growth factor 2 receptor (IGF-IIR) protein was developed. The gold substrate and silver nanoparticles (AgNPs) were employed simultaneously to achieve double enhancement for SERS signals. Firstly, the five commercial SERS substrates including Enspectr, Ocean-Au, Ocean-AG, Ocean-SP and Q-SERS substrates were evaluated using 4-mercaptobenzoic acid (4-MBA). The Q-SERS substrate was selected based on low relative standard deviation (RSD, 8.6%) and high enhancement factor (EF, 8.7*105), using a 785nm laser. The aptamer for IGF-IIR protein was designed to include two sequences: one grafted on gold substrate to specifically capture the IGF-IIR protein and a second one forming a 3' sticky bridge to capture SERS nanotags. The SERS nanotag was composed by AgNPs (20nm), 4-MBA and DNA probes that can hybridize with the aptamer. Due to the steric-hindrance effect, when the aptamer doesn't combine with IGF-IIR protein, it only can capture the SERS nanotags. Therefore, there was a negative correlation between the concentration of IGF-IIR protein and the intensity of 4-MBA at 1076cm-1. The detection limit reached to 141.2 fM and linear range was from 10 pM to 1μM. The SERS aptasensor also exhibits a high reproducibility with an average RSD of 4.5%. The interference test was conducted with other four proteins to verify the accuracy of measuring. The study provides an approach to quantitative determination of proteins based on specific recognition and nucleic acid hybridization of aptamers, to establish sandwich structure for SERS enhancement. Graphical abstractSchematic representation of surface-enhanced Raman scattering (SERS) assay on insulin-like growth factor 2 receptor (IGF-IIR) protein by combining the aptamer modified gold substrate and 4-mercaptobenzoic acid (4-MBA) and DNA probe modified silver nanoparticles.

Highly sensitive detection of influenza virus with SERS aptasensor.

Highly sensitive and rapid technology of surface enhanced Raman scattering (SERS) was applied to create aptasensors for influenza virus detection. SERS achieves 106−109 times signal amplification, yielding excellent sensitivity, whereas aptamers to hemagglutinin provide a specific recognition of the influenza virus. Aptamer RHA0385 was demonstrated to have essentially broad strain-specificity toward both recombinant hemagglutinins and the whole viruses. To achieve high sensitivity, a sandwich of primary aptamers, influenza virus and secondary aptamers was assembled. Primary aptamers were attached to metal particles of a SERS substrate, and influenza viruses were captured and bound with secondary aptamers labelled with Raman-active molecules. The signal was affected by the concentration of both primary and secondary aptamers. The limit of detection was as low as 1 · 10−4 hemagglutination units per probe as tested for the H3N2 virus (A/England/42/72). Aptamer-based sensors provided recognition of various influenza viral strains, including H1, H3, and H5 hemagglutinin subtypes. Therefore, the aptasensors could be applied for fast and low-cost strain-independent determination of influenza viruses.

Determination of Saxitoxin by Aptamer-Based Surface-Enhanced Raman Scattering

Saxitoxin is one of the most harmful paralytic shellfish toxins due to its high toxicity and adverse effects on the environment and human health. Aptasensors provide simple detection procedures because they have the advantages of chemical stability, easy synthesis and modification, and high convenience in signal transformation. Surface-enhanced Raman scattering (SERS) is an analytical technique that amplifies the analytical signals of molecules at extremely low concentrations, or even at the single molecule level, when the analyte is very close to rough metal surfaces or nanostructures. In this study, an SERS aptasensor is reported for the determination of saxitoxin for the first time. The optimized saxitoxin aptamer (M-30f) was modified on gold nanoparticles and served as the recognition element. Crystal violet was used as the Raman reporter without chemical bounding. The analytical principles of the aptasensor are that saxitoxin destabilized the conformations of the aptamer at high temperature conditions and altered the binding of crystal violet on the gold nanoparticles. In the presence of saxitoxin, the conformation of aptamer containing the G-quadruplex that selectively bound crystal violet unfolded to a large extent and hence the crystal violet molecules were released from gold nanoparticles with a reduced SERS signal. The effects of the gold nanoparticle size, the amount of DNA, aptamer density, sodium chloride concentration, and operation temperature upon the SERS determination were optimized. The resulting simple SERS aptasensor was developed with a satisfactory limit of detection (11.7 nM) and selectivity. The application for the analysis of real shellfish samples with simple procedures demonstrates that this SERS aptasensor is promising for on-site applications.