Ultrasensitive Detection Of Analytes Research Articles

Accelerated peroxidase-like activity of ultrathin amine-tagged bimetallic MOF-74 nanozyme for construction of versatile bioassays from small molecules to enzymes and bacteria

The exquisite design of nanostructures for enzyme-biocatalyzed active sites mimicking has become a prospective method to significantly boost biocatalytic properties, which is profitable to response amplification for bioanalysis scenarios. Metal-organic frameworks (MOFs) with customizable compositions, diverse microstructures and open catalytic sites are considered to deal with challenges in conventional materials of unfriendly microenvironment and inexact coordination. Herein, by combining a metal doping and post-synthetic modification approach, amine-tagged Fe-Ni bimetallic MOF-74 nanozyme (FeNi-MOF-74-NH2) with ultrathin structure and improved peroxidase-mimicking bioactivity is synthesized through a layered double hydroxide (LDH) directed method. The boosted biocatalytic property largely benefits from the synergistic effects of Fe-Ni species, attributing to the dual mechanism (electron transfer and generation of hydroxyl radicals). On the basis of the enhanced enzyme-mimicking property and accessible amino functionalization of FeNi-MOF-74-NH2, versatile applications were carried out for the ultrasensitive detection of analytes from bioactive small molecules (H2O2 and ascorbic acid), biomacromolecules (alkaline phosphatase, ascorbic acid oxidase, and α-glucosidase), and pathogenic bacteria (Staphylococcus aureus). The nanozyme-based biosensing platform without complex enzymatic techniques serves as a proof-of-concept to facilitate the application of MOF nanozymes in biochemical analysis, clinical diagnosis, and biomedical research.

Thiol-functionalized mesoporous silica-embedded AuNPs with highly sensitive substrates for surface-enhanced Raman scattering detection

Surface-enhanced Raman spectroscopy (SERS) provides a fast, simple, and label-free approach that can directly detect various analytes attached to SERS substrates and provide qualitative and quantitative information based on the SERS spectra of the analyte. The signal enhancement provided by noble metal particles allows us to achieve high sensitivity and good stability even at low concentrations in water quality testing. Over the past decade, SERS has become increasingly popular in the detection field, highlighting its significant application potential. However, the signal enhancement of single AuNPs is inferior to that of AgNPs, but we can achieve an overall enhancement by uniformly arranging multiple AuNPs. The hot-spot effect, which is crucial for Raman signal enhancement, occurs only when NMNPs are within a specific distance. However, when noble metal particles come into contact with each other, the enhancement effect of the hot spot disappears. Therefore, in this study, AuNPs@MPS-SH substrates with surface-enhanced Raman scattering (SERS) activity were successfully synthesized by immobilizing AuNPs on thiol-functionalized mesoporous silica (MPS-SH). MPS nanospheres with tailored pore size and surface-bound -SH groups were synthesized for the controlled embedding of Au nanoparticles (AuNPs). By adjusting the ratio of reactants, uniform AuNP dispersion and strong MPS-AuNP interactions were achieved. This optimized structure creates localized surface plasmon resonance (LSPR) hotspots, significantly enhancing the surface-enhanced Raman scattering (SERS) effect for ultrasensitive analyte detection. Transmission electron microscopy (TEM) revealed that the average diameter of MPS nanoparticles is 260 nm, with a pore size of 8 nm. Optimal Raman enhancement was achieved at an AuNPs concentration of 2.6 × 1018 particles/mL. The lowest detection limit concentration for Rhodamine 6G was below 10−6 M, while for uremic toxin (urea) it was below 10−3 M. The ability to directly detect low concentrations by mixing with the analyte demonstrates the ultra-high sensitivity and label-free detection potential of this study in the fields of water quality and disease detection.

Novel molecularly imprinted nanogel modified microfluidic paper-based SERS substrate for simultaneous detection of bisphenol A and bisphenol S traces in plastics

Paper-based surface-enhanced Raman scattering (SERS) optical nanoprobes provide ultrasensitive analyte detection; however, they lack selectivity, making them difficult to use in real-world sample analysis without a pretreatment process. This work describes the design of a microfluidic paper-based SERS substrate based on molecularly imprinted nanogels decorated with silver nanoparticles to simultaneously detect bisphenol A (BPA) and bisphenol S (BPS) traces in plastic toys and receipts. The synthesized nanogels have two characteristics that boost SERS performance: molecularly imprinted cavities that allow for selective adsorption and a wrinkled surface that creates uniformly distributed hot spots. Simple paper-based sensor devices were built as ‘drop and read’ SERS substrates with a separate reservoir to detect a single target, while advanced SERS platforms were designed as a microfluidic chip with two reservoirs connected by a channel for simultaneous detection of BPA and BPS. The SERS platform with a single reservoir showed outstanding analytical performance for the detection of BPA and BPS, with low detection limits of 0.38 pM and 0.37 pM, respectively. The microfluidic paper-based sensor allowed simultaneous and selective detection of BPA and BPS with detection limits estimated at 0.68 nM and 0.47 nM, respectively. The developed sensors are successfully applied to detect BPA and BPS in plastic products and receipts. Finally, the results obtained with our method showed greater sensitivity than those of commercially available ELISA kits, and the acquired values within the ELISA detection range were in excellent agreement.

Microfluidic-Assisted Alignment of Graphene Nanosheets for Microfiber Formation

Recently, our lab developed graphene oxide microfibers for ultrasensitive neurochemical detection with fast-scan cyclic voltammetry (FSCV). Graphene-fiber microelectrodes provide a significant advance over traditional carbon-fiber microelectrodes due to their resistance to detrimental fouling, fast electron transfer kinetics, and frequency independent behavior. Despite our recent advancement, there still exists a gap in our understanding of how specific changes in the carbon chemical structure influences adsorption and interaction of various neurochemicals at the surface. Understanding the extent to which the carbon chemical structure influences electrochemical detection is critical for designing tailor-made electrodes for ultrasensitive analyte detection. From a molecular level point-of-view, the graphene sheet consists of two regions with different structure: i) the basal plane, consisting of conjugated sp2 hybridized carbon atoms, and characterized by an atomic flatness and low defect density; and ii) the edge plane, that forms sp3 sites with a high level of defects and a variety of functional groups and dangling bonds. It is generally believed that the electrochemical properties of the basal and edge plane are significantly different, however, there has been debate concerning the electrochemical activity at the basal and edge plane. The conventional consensus is that electron transfer kinetics is faster on the edge plane in comparison with the basal plane sites, while the opposite barrier of this debate provides evidence for fast electron transfer at pristine basal plane. Moreover, how these factors influence neurochemical detection, particularly at rapid scan rates, is still lacking due to the necessity of using microelectrodes with FSCV. To date, most studies analyzing the influence of basal vs. edge plane surfaces on electrochemical detection have used macroelectrodes like highly ordered pyrolytic graphite (HOPG) which are not amenable to FSCV detection due to the large capacitive currents obtained at macroelectrodes at scan rates consisting of hundreds of volts per second. Therefore, to address this existing knowledge gap in understanding how edge vs. basal planes influence subsecond neurochemical detection, the ability to develop microelectrodes with controlled surfaces is crucial. Here, I will discuss our labs latest effort in developing graphene oxide microfibers with controllable nanosheet alignment to study the influence of basal vs. edge plane availability on neurochemical detection at rapid scan rates. To assist in nanosheet alignment, we use microfluidic channels to assist in fluid-driven control of nanosheet orientation. Using microfluidics to help develop highly controllable electrode materials provides a critical advance in our ability to develop novel carbon surfaces for detection.

Ultrasensitive detection of thiram based on surface-enhanced Raman scattering via Au@Ag@Ag core/shell/shell bimetallic nanorods.

We developed a highly sensitive and stable SERS-active substrate of Au@Ag@Ag core/shell/shell nanorods, formed by encapsulating Au nanorods (Au NRs) into a bilayer silver shell with Raman reporter molecules (4-mercaptobenzoic acid (4-MBA) and thiram) in the shell-shell gap. The core/shell/shell nanostructures demonstrated a high SERS enhancement and easy assembly. The important role of the bilayer silver shell in boosting the SERS intensity and detection sensitivity was revealed by comparing the performances of the Au@Ag@4-MBA@Ag NRs, Au@Ag@4-MBA NRs, and Au@4-MBA NRs. The obtained Au@Ag@4-MBA@Ag NRs exhibited a significantly promoted SERS intensity, which could reach around 2.6 times and 240 times that of the Au@Ag@4-MBA NRs and Au@4-MBA NRs, where the enhancement factor was found to be strongly correlated with the shell thickness. The controllable plasma properties and SERS effect of the Au@Ag@4-MBA@Ag NRs could be optimized by adjusting the dose of silver nitrate. The SERS substrate comprising core/shell/shell nanorods was highly reproducible and stable (retaining 83% SERS intensity after one month). Moreover, the highly sensitive detection of the pesticide thiram with a detection limit as low as 1.74 × 10-9 M was achieved by taking advantage of the great SERS response of the core/shell/shell nanostructures, which was 1-2 orders of magnitude lower than for other SERS substrates. The developed SERS substrate could be readily extended to embed other target analytes into the core/shell/shell nanostructure for novel and sensitive detection. This study could enable fresh approaches toward next-generation ultrasensitive analyte detection.

Flow‐Based Synthesis of Gold‐Coated Magnetic Nanoparticles for Magnetoplasmonic Sensing Applications

Gold-coated magnetic nanoparticles are key materials for the fast separation and ultrasensitive detection of analytes in magnetoplasmonic sensors. However, the synthesis of gold-coated magnetic nanoparticles typically requires small-scale, colloidal methods over hours or days and often results in incomplete shells with variable optical properties. A robust, rapid, and scalable synthesis method is still needed to reliably form a complete gold nanoshell around magnetic nanoparticles. Herein, a new methodology for the synthesis of gold-coated magnetic nanoparticles via a flow-based manufacturing system that can easily be scaled up is presented. The developed method first produces gold-seeded silica coated magnetic nanoparticles and then a complete, tunable gold shell with relatively uniform size and shape. The flow-based method can be performed in a total time of less than 2 min, enabling rapid and complete gold coating. The particles show both excellent magnetic and plasmonic properties, which facilitates application as biosensing agents in dark-field microscopy and surface-enhanced Raman scattering.

Activators Confined Upconversion Nanoprobe with Near-Unity Förster Resonance Energy Transfer Efficiency for Ultrasensitive Detection

Lanthanide-doped upconversion nanoparticles (UCNPs) as energy donors for Förster resonance energy transfer (FRET) are promising in biosensing, bioimaging, and therapeutic applications. However, traditional FRET-based UC nanoprobes show low efficiency and poor sensitivity because only partial activators in UCNPs possessing suitable distance with energy acceptors (<10 nm) can activate the FRET process. Herein, a novel excited-state energy distribution-modulated upconversion nanostructure is explored for highly efficient FRET. Integration of the optimal 4% Er3+ doped shell and 100% Yb3+ core achieves ∼4.5-fold UC enhancement compared with commonly used NaYF4:20%Yb3+,2%Er3+ nanoparticles, enabling maximum donation of excitation energy to an acceptor. The spatial confinement strategy shortens significantly the energy-transfer distance (∼4.5 nm) and thus demonstrates experimentally a 91.9% FRET efficiency inside the neutral red (NR)-conjugated NaYbF4@NaYF4:20%Yb3+,4%Er3+ nanoprobe, which greatly outperforms the NaYbF4@NaYF4:20%Yb3+,4%Er3+@SiO2@NR nanoprobe (27.7% efficiency). Theoretical FRET efficiency calculation and in situ single-nanoparticle FRET measurement further confirm the excellent energy-transfer behavior. The well-designed nanoprobe shows a much lower detection limit of 0.6 ng/mL and higher sensitivity and is superior to the reported NO2- probes. Our work provides a feasible strategy to exploit highly efficient FRET-based luminescence nanoprobes for ultrasensitive detection of analytes.

Revealing interfacial charge transfer in TiO2/reduced graphene oxide nanocomposite by surface-enhanced Raman scattering (SERS): Simultaneous a superior SERS-active substrate

The strong interface interaction, especially interfacial charge transfer (CT) behavior, in TiO2/reduced graphene oxide (TiO2/rGO) nanocomposite endows the advanced hybrid material with extensive availability in dye-sensitized solar cells, photocatalysis, etc. Thus, revealing and understanding of the interfacial CT process are a crucial and interesting issue, owing to its vital contributions to optoelectronic and electronic properties. In this work, the TiO2/rGO nanocomposites with anchoring of TiO2 nanoparticles on rGO nanosheets have been fabricated, and a surface-enhanced Raman scattering (SERS) strategy with 4-mercaptobenzoic acid (4-MBA) as probe was performed to reveal the interfacial CT in the nanocomposites. There are obvious enhancements in the SERS intensity and the degree of CT (ρCT) in the 4-MBA/TiO2/rGO/4-MBA system compared with those of 4-MBA/TiO2 and 4-MBA/TiO2 + rGO/4-MBA (TiO2 + rGO is a physical mixture of TiO2 and rGO) due to the chemical interaction and the interfacial CT between TiO2 and rGO in the nanocomposite. It is indicated that the interfacial chemical interaction in the nanocomposite is an essential requirement for occurrence of the interfacial CT. The interfacial CT process can be evaluated quantitatively by the ρCT in SERS spectrum. The ρCT shows an obvious increasing trend with the increase of rGO amount in TiO2/rGO nanocomposites, and then reaches a saturation when the amount of rGO is 1.0%. And also, to further understanding of this CT progress, the model of the CT mechanism has been proposed. Furthermore, as-prepared TiO2/rGO nanocomposite can also be served as an effective SERS-active substrate for the ultrasensitive detection of analytes. The minimum detectable concentration of 4-MBA on the TiO2/rGO substrate can reach to 1 × 10−7 mol/L, which is comparable to a noble metal substrate. Even, for p-aminothiophenol target molecule whose SERS signals cannot almost be observed on the ordinary TiO2 substrate, the minimum detectable concentration can reach to a value as low as 1 × 10−8 mol/L on the TiO2/rGO substrate.

Single-Molecule Kinetic Fingerprinting for the Ultrasensitive Detection of Small Molecules with Aptasensors.

Aptamers have emerged as promising molecular tools for small-molecule analyte sensing. However, the performance of such aptasensors is generally limited by leakage since it has been difficult to completely suppress signal in the absence of analyte, resulting in a compromise between sensitivity and specificity. Here, we describe a methodology for the ultrasensitive detection of analytes combining aptasensors with single-molecule kinetic fingerprinting. A short, fluorescently labeled DNA probe is utilized to detect the structural changes upon ligand binding to the designed hairpin-shaped aptasensor probe. The Poisson statistics of binding and dissociation events of the DNA probe to single surface-immobilized aptasensor molecules is monitored by total internal reflection fluorescence microscopy, permitting the high-accuracy discrimination of the ligand bound and ligand-free states, resulting in zero background. The programmable dynamics of the hairpin enables fine-tuning of the hybridization kinetics of the fluorescent probe, rendering the acquisition time sufficiently flexible to optimize discrimination. Remarkable detection limits are achieved for a diverse set of analytes when spiked into chicken meat extract: the nucleotide adenosine (0.3 pM), the insecticide acetamiprid (0.35 pM), and the dioxin-like toxin PCB-77 (0.72 pM), which is superior to recently reported aptasensors. Our generalizable method significantly improves the performance of aptasensors, with the potential to extend to other molecular biomarkers.

"On-Off-On" Photoelectrochemical/Visual Lab-on-Paper Sensing via Signal Amplification of CdS Quantum Dots@Leaf-Shape ZnO and Quenching of Au-Modified Prism-Anchored Octahedral CeO2 Nanoparticles.

An effective"on-off-on" photoelectrochemical (PEC)/visual sensing system based on cleaning-switchable lab-on-paper device was designed to achieve ultrasensitive detection of analytes. The first amplified "signal-on" PEC state was gained by CdS quantum dots sensitized leaf-shape ZnO (CdS QDs/leaf-shape ZnO) structure, which was assembled on reduced graphene oxide (rGO) modified paper electrode. Then Au-modified prism-anchored octahedral CeO2 nanoparticles (Au@PO-CeO2 NPs), as an efficient signal quencher, were immobilized on the CdS QDs/leaf-shape ZnO with the assistance of DNA hybridization, resulting in a noticeable photocurrent response decrement with the "signal-off" PEC state. With the addition of analytes, the quencher Au@PO-CeO2 NPs were immediately released from the sensing surface and robust PEC response was recovered to the signal-on state again. Meanwhile, the disengaged quencher in electrolyte solution flowed to the colorimetric detection area of lab-on-paper device and catalyzed oxidation of the chromogenic substrate 3,3',5,5'-tetramethylbenzidine in the presence of H2O2 to form the colored product, making the analytes detection more convincing with the visual discrimination. Under optimal conditions, the proposed PEC/visual lab-on-paper device possessed the detection limits toward adenosine and potassium ion as low as 0.15 and 0.06 nM, respectively. With ingenious design of actuating conversion process between hydrophilicity and hydrophobicity by slipping paper tab to solve cleaning issue in the assay procedures, the cleaning-switchable lab-on-paper device was constructed for high-performance biosensing applications. It provides an unambiguous simplicity and portable operation for exploring high reliability and sensitivity of novel point-of-care diagnostic tool with dual-signal readout.

SERS-from-scratch: An electric field-guided nanoparticle assembly method for cleanroom-free and low-cost preparation of surface-enhanced Raman scattering substrates

Ultrasensitive detection of analytes is important in forensic science, environmental monitoring and medical diagnostics. Surface-enhanced Raman scattering (SERS) is an analytical detection method with single-molecule sensitivity, but nanofabrication of SERS substrates poses a barrier to its application. Here, we report on a facile and rapid approach to prepare ultrasensitive SERS substrates in situ by using electrokinetics to assemble Ag nanoparticles on a scored conductive surface. We demonstrate the unique characteristic of our method to produce highly SERS-active surfaces from a wide range of materials, including commercially available glass slides pre-coated with indium tin oxide (ITO). We show that the “SERS from scratch” substrates can detect trace quantities of explosives, drugs and pesticides, with sensitivities superior to some commercially available products.

Silica-Coated Plasmonic Metal Nanoparticles in Action.

Hybrid colloids consisting of noble metal cores and metal oxide shells have been under intense investigation for over two decades and have driven progress in diverse research lines including sensing, medicine, catalysis, and photovoltaics. Consequently, plasmonic core-shell particles have come to play a vital role in a plethora of applications. Here, an overview is provided of recent developments in the design and utilization of the most successful class of such hybrid materials, silica-coated plasmonic metal nanoparticles. Besides summarizing common simple approaches to silica shell growth, special emphasis is put on advanced synthesis routes that either overcome typical limitations of classical methods, such as stability issues and undefined silica porosity, or grant access to particularly sophisticated nanostructures. Hereby, a description is given, how different types of silica can be used to provide noble metal particles with specific functionalities. Finally, applications of such nanocomposites in ultrasensitive analyte detection, theranostics, catalysts, and thin-film solar cells are reviewed.

A White Light-Emitting Quantum Dot Complex for Single Particle Level Interaction with Dopamine Leading to Changes in Color and Blinking Profile.

The interaction of the neurotransmitter dopamine is reported with a single particle white light-emitting (WLE) quantum dot complex (QDC). The QDC is composed of yellow emitting ZnO quantum dots (Qdots) and blue emitting Zn(MSA)2 complex (MSA = N-methylsalicylaldimine) synthesized on their surfaces. Sensing is achieved by the combined changes in the visual luminescence color from white to blue, chromaticity color coordinates from (0.31, 0.33) to (0.24, 0.23) and the ratio of the exponents (αon /αoff ) of on/off probability distribution (from 0.24 to 3.21) in the blinking statistics of WLE QDC. The selectivity of dopamine toward ZnO Qdots, present in WLE QDC, helps detect ≈13 dopamine molecules per Qdot. Additionally, the WLE QDC exhibits high sensitivity, with a limit of detection of 3.3 × 10-9 m (in the linear range of 1-100 × 10-9 m) and high selectivity in presence of interfering biological species. Moreover, the single particle on-off bilking statistics based detection strategy may provide an innovative way for ultrasensitive detection of analytes.

Ultrasensitive Analyte Detection by Combining Nanoparticle-based Surface-Enhanced Raman Scattering (SERS) Substrates with Multivariate Analysis

A facile and rapid method for the in situ fabrication of highly active surface-enhanced Raman scattering (SERS) substrates is presented. These SERS-active substrates are produced on the surface of microelectrode chips through an electric field-guided assembly of silver nanocolloids, which yields highly branched, dendritic nanoparticle structures. Fractal dimension analysis of the dendrites shows a value of 1.78, indicating a high degree of complexity. The sensitivity of the SERS substrates is demonstrated with the detection of trace amounts of cocaine in water. By analyzing the collected spectra using principal component analysis, spectra can be correctly identified and quantified in an automated fashion for several different concentrations

Aptamer-Embedded Zirconium-Based Metal-Organic Framework Composites Prepared by De Novo Bio-Inspired Approach with Enhanced Biosensing for Detecting Trace Analytes.

A series of Zr-based metal-organic framework (MOF) composites embedded with three kinds of aptamer strands (509-MOF@Apt) were achieved by a one-step de novo synthetic approach. A platform for ultrasensitive detection of analytes, namely, thrombin, kanamycin, and carcinoembryonic antigen (CEA), was also established. Considering the conformational changes caused by the binding interactions between aptamer strands and targeted molecules, the label-free electrochemical aptasensors based on 509-MOF@Apt composites could be developed to detect various target molecules. By comparing the common fabrication approaches of aptasensors, a distinct determination mechanism was presented through analysis of the electrochemical measurements on different interaction behaviors between probe aptamer strands and 509-MOF materials. The optimized aptasensors based on 509-MOFs@Apt demonstrated excellent sensitivity (with the detection limit of 0.40, 0.37, and 0.21 pg mL-1 for CEA, thrombin, and kanamycin, respectively), stability, repeatability, and applicability. This work will provide a new platform for direct and feasible detection in biosensing related to clinical diagnostics and therapeutics, and further, extend the scope of potential applications for MOF materials.

Analysis of Serotonin Molecules on Silver Nanocolloids-A Raman Computational and Experimental Study.

Combined theoretical and experimental analysis of serotonin by quantum chemical density functional calculations and surface-enhanced Raman spectroscopy, respectively, is presented in this work to better understand phenomena related to this neurotransmitter’s detection and monitoring at very low concentrations specific to physiological levels. In addition to the successful ultrasensitive analyte detection on silver nanoparticles for concentrations as low as 10−11 molar, the relatively good agreement between the simulated and experimentally determined results indicates the presence of all serotonin molecular forms, such as neutral, ionic, and those oxidized through redox reactions. Obvious structural molecular deformations such as bending of lateral amino chains are observed for both ionic and oxidized forms. Not only does this combined approach reveal more probable adsorption of serotonin into the silver surface through hydroxyl/oxygen sites than through NH/nitrogen sites, but also that it does so predominantly in its neutral (reduced) form, somewhat less so in its ionic forms, and much less in its oxidized forms. If the development of opto-voltammetric biosensors and their effective implementation is envisioned for the future, this study provides some needed scientific background for comprehending changes in the vibrational signatures of this important neurotransmitter.

How nanotechnology-enabled concepts could contribute to the prevention, diagnosis and therapy of bacterial infections.

This viewpoint summarizes a selection of nanotechnology-based key concepts relevant to critical care medicine. It focuses on novel approaches for a trigger-dependent release of antimicrobial substances from degradable nano-sized carriers, the ultra-sensitive detection of analytes in body fluid samples by plasmonic and fluorescent nanoparticles, and the rapid removal of pathogens from whole blood using magnetic nanoparticles. The concepts presented here could significantly contribute to the prevention, diagnosis and therapy of bacterial infections in future and it is now our turn to bring them from the bench to the bedside.

Aggregated Silver Nanoparticles Based Surface-Enhanced Raman Scattering Enzyme-Linked Immunosorbent Assay for Ultrasensitive Detection of Protein Biomarkers and Small Molecules

Lowering the detection limit is critical to the design of bioassays required for medical diagnostics, environmental monitoring, and food safety regulations. The current sensitivity of standard color-based analyte detection limits the further use of enzyme-linked immunosorbent assays (ELISAs) in research and clinical diagnoses. Here, we demonstrate a novel method that uses the Raman signal as the signal-generating system of an ELISA and combines surface-enhanced Raman scattering (SERS) with silver nanoparticles aggregation for ultrasensitive analyte detection. The enzyme label of the ELISA controls the dissolution of Raman reporter-labeled silver nanoparticles through hydrogen peroxide and generates a strong Raman signal when the analyte is present. Using this assay, prostate-specific antigen (PSA) and the adrenal stimulant ractopamine (Rac) were detected in whole serum and urine at the ultralow concentrations of 10(-9) and 10(-6) ng/mL, respectively. The methodology proposed here could potentially be applied to other molecules detection as well as PSA and Rac.

Ultrasensitive detection of single nucleotide polymorphism in human mitochondrial DNA utilizing ion-mediated cascade surface-enhanced Raman spectroscopy amplification.

Although surface-enhanced Raman spectroscopy (SERS) has been featured by high sensitivity, additional signal enhancement is still necessary for trace amount of biomolecules detection. In this paper, a SERS amplified approach, featuring "ions-mediated cascade amplification (IMCA)", was proposed by utilizing the dissolved silver ions (Ag(+)) from silver nanoparticles (AgNPs). We found that using Ag(+) as linkage agent can effectively control the gaps between neighboring 4-aminobenzenethiol (4-ABT) encoded gold nanoparticles (AuNPs@4-ABT) to form "hot spots" and thus produce SERS signal output, in which the SERS intensity was proportional to the concentration of Ag(+). Inspired by this finding, the IMCA was utilized for ultrasensitive detection of single nucleotide polymorphism in human mitochondrial DNA (16189T → C). Combining with the DNA ligase reaction, each target DNA binding event could successfully cause one AgNP introduction. By detecting the dissolved Ag(+) from AgNPs using IMCA, low to 3.0 × 10(-5) fm/μL targeted DNA can be detected, which corresponds to extractions from 200 nL cell suspension containing carcinoma pancreatic β-cell lines from diabetes patients. This IMCA approach is expected to be a universal strategy for ultrasensitive detection of analytes and supply valuable information for biomedical research and clinical early diagnosis.

Rational design of a bisphenol A aptamer selective surface-enhanced Raman scattering nanoprobe.

Surface-enhanced Raman scattering (SERS) optical nanoprobes offer a number of advantages for ultrasensitive analyte detection. These functionalized colloidal nanoparticles are a multifunctional assay component. providing a platform for conjugation to spectral tags, stabilizing polymers, and biorecognition elements such as aptamers or antibodies. We demonstrate the design and characterization of a SERS-active nanoprobe and investigate the nanoparticles’ biorecognition capabilities for use in a competitive binding assay. Specifically, the nanoprobe is designed for the quantification of bisphenol A (BPA) levels in the blood after human exposure to the toxin in food and beverage plastic packaging. The nanoprobes demonstrated specific affinity to a BPA aptamer with a dissociation constant Kd of 54 nM, and provided a dose-dependent SERS spectra with a limit of detection of 3 nM. Our conjugation approach shows the versatility of colloidal nanoparticles in assay development, acting as detectable spectral tagging elements and biologically active ligands concurrently.