Au-NPs enhanced SPR biosensor based on hairpin DNA without the effect of nonspecific adsorption

Surface Plasmon Resonance Sensor Based on Fe2O3/Au for Alcohol Concentration Detection

Hematite (α-Fe2O3) is widely used in sensor sensitization due to its excellent optical properties. In this study, we present a sensitivity-enhanced surface plasmon resonance alcohol sensor based on Fe2O3/Au. We describe the fabrication process of the sensor and characterize its structure. We conduct performance testing on sensors coated multiple times and use solutions with the same gradient of refractive indices as the sensing medium. Within the refractive index range of 1.3335-1.3635, the sensor that was coated twice achieved the highest sensitivity, reaching 2933.2 nm/RIU. This represents a 30.26% enhancement in sensitivity compared to a sensor with a pure gold monolayer film structure. Additionally, we demonstrated the application of this sensor in alcohol concentration detection by testing the alcohol content of common beverages, showing excellent agreement with theoretical values and highlighting the sensor's potential in food testing.

Ultrasensitive detection of SARS-CoV-2 nucleocapsid protein using large gold nanoparticle-enhanced surface plasmon resonance

The COVID-19 pandemic has created urgent demand for rapid detection of the SARS-CoV-2 coronavirus. Herein, we report highly sensitive detection of SARS-CoV-2 nucleocapsid protein (N protein) using nanoparticle-enhanced surface plasmon resonance (SPR) techniques. A crucial plasmonic role in significantly enhancing the limit of detection (LOD) is revealed for exceptionally large gold nanoparticles (AuNPs) with diameters of hundreds of nm. SPR enhanced by these large nanoparticles lowered the LOD of SARS-CoV-2 N protein to 85 fM, resulting in the highest SPR detection sensitivity ever obtained for SARS-CoV-2 N protein.

DNA cyclic assembling control in an electrochemical strategy with MoS2@AuNPs for determination of kanamycin

A sensitive electrochemical strategy was established for kanamycin determination. A specific aptamer was modified on the electrode as the probe, followed by a cyclic hybridization chain reaction (HCR) with methylene blue, causing an increasing signal response. In the presence of kanamycin, it can initiatively convolve the aptamer and prevent further DNA assembling, resulting in a signal distinction sensitive to the target amount. However, the signal reproducibility is low. To improve the precision, the HCR procedure was investigated. The results demonstrated that the optimal amount of assembled DNA is 12-fold to that of aptamer. This amount was then controlled in further assays. Admittedly, controlled DNA assembling commonly indicates a limited signal amplification. To further enhance the sensitivity, a nanocomposite based on MoS₂ and AuNPs was modified on the electrode. The results of the assay proved that the signal distinction sensitive to target amount increased by 50%. A linearity range is obtained from 0.01 nM to 1.0 μM of kanamycin, and the LOD is 8.4 pM. Subsequently, this strategy was employed to detect kanamycin in chicken liver and milk sample; the recovery results suggest that it possess a satisfactory application prospect in analysis of agricultural products.

A lable-free SPR biosensor based on one peptide sequence with three recognition sites for O-GlcNAc transferase detection

Abnormal O-linked N-acetylglucosamine (O-GlcNAc) concentrations have been associated with many diseases, but the lack of accurate detection method limited O-GlcNAc to be used as a biomarker in clinical diagnosis. Then O-GlcNAc transferase (OGT) has drawn researchers' attention as it closed related to the level of O-GlcNAc and be considered to be a promising new target for diseases diagnosis. Nevertheless, the existing OGT detection methods are either need labeling or the sensitity can not meet the needs of clinic testing. Herein, a label-free and sensitive SPR biosensor was developed for accurate detection of OGT based on a multi-functional peptide. The designed peptide contains three recognition sites, one is the cleavage site of protease K, one is the O-GlcNAcylated site by OGT, and another is six histidine which be used as the signal report probe to recognize Ni²⁺. The immobilized peptide would be cleavaged by proteinase K, then the His-tag residue part will leave the surface of Au film, resulting less His-tag could bind to Ni²⁺ and a small SPR signal would be record. If the peptide is O-GlcNAcylated by OGT, the cleaving reaction would be limited due to the adjacent site of O-GlcNAcylation. Then more His-tag can be left on the Au film and a bigger SPR signal could be record, this signal is associated with the concentration of OGT. Utilizing the change of the peptide configuration as a signal report probe for OGT detection not only avoids labeling of peptide, but also makes the method more sensitive. The determination linear range of OGT is from 2.00 × 10^-13 to 5.00 × 10^-8 M with a detection limit of 1.19 × 10^-13 M, and the separation of two enzyme reactions ensured the high selectivity of the method. Finally, the sensing system was successfully used for OGT detection in blood samples with satisfied recovery. In summary, the label-free SPR platform for accurate detection of OGT in real samples is helpful to promote OGT serve as a biomarker for early clinical diagnosis of O-GlcNAc related diseases.

Ultrasensitive Detection of Bacterial Protein Toxins on Patterned Microarray via Surface Plasmon Resonance Imaging with Signal Amplification by Conjugate Nanoparticle Clusters

Sensitive detection and monitoring of biological interactions in a high throughput, multiplexed array format has numerous advantages. We report here a method to enhance detection sensitivity in surface plasmon resonance (SPR) spectroscopy and SPR imaging via the effect of accumulation of conjugated nanoparticles of varying sizes. Bacterial cholera toxin (CT) was chosen for the demonstration of enhanced immunoassay by SPR. After immobilization of CT on a gold surface, specific recognition is achieved by biotinylated anti-CT. The signal is amplified by the attachment of biotinylated 20 nm AuNP via streptavidin bridge, followed by attachment of 5 nm streptavidin-functionalized Fe₃O₄NP to the AuNP-biotin surface. The continuous surface binding of two differently sized conjugated nanoparticles effectively increases their packing density on surface and significantly improves SPR detection sensitivity, allowing quantitative measurement of CT at very low concentration. The dense packing of conjugated nanoparticles on the surface was confirmed by atomic force microscopy characterization. SPR imaging of the immunoassay for high-throughput analysis utilized an Au-well microarray that attenuated the background resonance interference on the resulting images. A calibration curve of conjugated nanoparticle binding signal amplification for CT detection based on surface coverage has been obtained that shows a correlation in a range from 6.31 × 10^-16 to 2.51 × 10^-13 mol/cm² with the limit of detection of 5.01 × 10^-16 mol/cm². The absolute quantity of detection limit using SPR imaging was 0.25 fmol. The versatile nanoparticles and biotin-streptavidin interaction used here should allow adaptation of this enhancement method to many other systems that include DNA, RNA, peptides, and carbohydrates, opening new avenues for ultrasensitive analysis of biomolecules.

Surface plasmon resonance biosensor for the accurate and sensitive quantification of O-GlcNAc based on cleavage by β-D-N-acetylglucosaminidase

Abnormal O-linked-N-acetylglucosamine (O-GlcNAc) concentrations have been associated with a variety of diseases (e.g., cancer, Alzheimer's disease, cardiovascular disease, etc.). However, O-GlcNAc detection is complicated, time-consuming and has poor specificity, therefore, the accurate detection of O-GlcNAc is difficult. In this study, an accurate and sensitive surface plasmon resonance (SPR) biosensor for O-GlcNAc detection that is based on β-D-N-acetylglucosaminidase (OGA) and Au nanoparticles (AuNPs) was developed. In this strategy, AuNPs were used to amplify the SPR signal and improve the biosensor's sensitivity; OGA was used to cleave O-GlcNAc from O-GlcNAcylated biomolecules. The interaction between AuNPs labeled wheat germ agglutinin (AuNPs/WGA) and O-GlcNAcylated biomolecules on a modified Au film treated with and without OGA was recorded by SPR. The change of the SPR signal moves linearly with the amount of O-GlcNAc on the Au film and thus could be used for the detection of O-GlcNAc. By recording the difference of the SPR signals, this method can avoid disturbances from other sugars and nonspecific adsorption of AuNPs and thus enable the accurate detection of O-GlcNAc. The accurate detection range of O-GlcNAc was 4.65 × 10^-12 to 4.65 × 10^-7 M which was obtained by quantifying the amount of a standard O-GlcNAcylated peptide (O-GlcNAc-CREB), and the detection limit is 4.65 × 10^-13 M. More importantly, the strategy was successfully used to detect O-GlcNAc in a real α-crystallin protein, cancer cell lysates and blood samples with satisfactory results. The study's results imply that this accurate and sensitive method has the potential to be applied in the early clinical diagnosis of O-GlcNAc-related diseases.

A simple surface plasmon resonance biosensor for detection of PML/RARα based on heterogeneous fusion gene-triggered nonlinear hybridization chain reaction

In this work, a simple and enzyme-free surface plasmon resonance (SPR) biosensing strategy has been developed for highly sensitive detection of two major PML/RARα (promyelocytic leukemia, retinoic acid receptor alpha) subtypes based on the heterogeneous fusion gene-triggered nonlinear hybridization chain reaction (HCR). On the gold chip surface, the cascade self-assembly process is triggered after the introduction of PML/RARα. The different fragments of PML/RARα can specifically hybridize with capture probes (Cp) immobilized on the chip and the hybridization DNA₁ (H₁). Then, the nonlinear HCR is initiated by the complex of Cp-PML/RARα-H₁ with the introduction of two hybridization DNA chains (H₂ and H₃). As a result, a dendritic nanostructure is achieved on the surface of chip, leading to a significant SPR amplification signal owing to its high molecular weight. The developed method shows good specificity and high sensitivity with detection limit of 0.72 pM for "L" subtype and 0.65 pM for "S" subtype. Moreover, this method has been successfully applied for efficient identification of clinical positive and negative PCR samples of the PML/RARα subtype. Thus, this developed biosensing strategy presents a potential platform for analysis of fusion gene and early diagnosis of clinical disease.

High-sensitive surface plasmon resonance microRNA biosensor based on streptavidin functionalized gold nanorods-assisted signal amplification

Herein, a facile and sensitive microRNA (miRNA) biosensor was designed by using interfacial biotinylated thiolated DNA molecular beacon (MB) as probe and streptavidin functionalized gold nanorods (Stre-GNRs) as tag for the enhanced surface plasmon resonance (SPR) signal. The MB probe with two terminals labeled with biotin and thiol groups, respectively, was modified on the gold film via thiol-gold interaction. Upon hybridization with the target, the biotinylated group became accessible to the Stre-GNRs. The introduction of the Stre-GNRs tag to the gold film produced strong SPR signal for detection. Our work has illustrated that the plasmonic field extension generated from the gold film to GNRs and the mass increase due to the GNRs have led to drastic sensitivity enhancement. Under optimal conditions, this proposed approach allowed detection of miRNA with the limit of detection (LOD) down to 0.045 pM. The results have shown that the MB probe functionalized sensing film, together with streptavidin-conjugated GNRs, was readily served as a plasmonic coupling partner that can be used as a powerful ultrasensitive sandwich assay for miRNA detection, and GNRs were readily served as promising amplification labels in SPR sensing technology.

Application of nanomaterials in the bioanalytical detection of disease-related genes

In the diagnosis of genetic diseases and disorders, nanomaterials-based gene detection systems have significant advantages over conventional diagnostic systems in terms of simplicity, sensitivity, specificity, and portability. In this review, we describe the application of nanomaterials for disease-related genes detection in different methods excluding PCR-related method, such as colorimetry, fluorescence-based methods, electrochemistry, microarray methods, surface-enhanced Raman spectroscopy (SERS), quartz crystal microbalance (QCM) methods, and dynamic light scattering (DLS). The most commonly used nanomaterials are gold, silver, carbon and semiconducting nanoparticles. Various nanomaterials-based gene detection methods are introduced, their respective advantages are discussed, and selected examples are provided to illustrate the properties of these nanomaterials and their emerging applications for the detection of specific nucleic acid sequences.

Nanomaterials enhanced surface plasmon resonance for biological and chemical sensing applications

The main challenge for all electrical, mechanical and optical sensors is to detect low molecular weight (less than 400 Da) chemical and biological analytes under extremely dilute conditions. Surface plasmon resonance sensors are the most commonly used optical sensors due to their unique ability for real-time monitoring the molecular binding events. However, their sensitivities are insufficient to detect trace amounts of small molecular weight molecules such as cancer biomarkers, hormones, antibiotics, insecticides, and explosive materials which are respectively important for early-stage disease diagnosis, food quality control, environmental monitoring, and homeland security protection. With the rapid development of nanotechnology in the past few years, nanomaterials-enhanced surface plasmon resonance sensors have been developed and used as effective tools to sense hard-to-detect molecules within the concentration range between pmol and amol. In this review article, we reviewed and discussed the latest trend and challenges in engineering and applications of nanomaterials-enhanced surface plasmon resonance sensors (e.g., metallic nanoparticles, magnetic nanoparticles, carbon-based nanomaterials, latex nanoparticles and liposome nanoparticles) for detecting "hard-to-identify" biological and chemical analytes. Such information will be viable in terms of providing a useful platform for designing future ultrasensitive plasmonic nanosensors.

Highly sensitive detection of human cardiac myoglobin using a reverse sandwich immunoassay with a gold nanoparticle-enhanced surface plasmon resonance biosensor

A highly sensitive reverse sandwich immunoassay for the detection of human cardiac myoglobin (cMb) in serum was designed utilizing a gold nanoparticle (AuNP)-enhanced surface plasmon resonance (SPR) biosensor. First, a monoclonal anti-cMb antibody (Mab1) was covalently immobilized on the sensor surface. AuNPs were covalently conjugated to the second monoclonal anti-cMb antibody (Mab2) to form an immuno-gold reagent (Mab2-AuNP). The reverse sandwich immunoassay consists of two steps: (1) mixing the serum sample with Mab2-AuNP and incubation for the formation of cMb/Mab2-AuNP complexes and (2) sample injection over the sensor surface and evaluation of the Mab1/cMb/Mab2-AuNP complex formation, with the subsequent calculation of the cMb concentration in the serum. The biosensor signal was amplified approximately 30-fold compared with the direct reaction of cMb with Mab1 on the sensor surface. The limit of detection of cMb in a human blood serum sample was found to be as low as 10 pM (approx. 0.18 ng mL(-1)), and the inter-assay coefficient of variation was less than 3%. Thus, the developed SPR-based reverse sandwich immunoassay has a sensitivity that is sufficient to measure cMb across a wide range of normal and pathological concentrations, allowing an adequate estimation of the disease severity and the monitoring of treatment.

Nanoscale sensor analysis using the immersed molecular electrokinetic finite element method

The concentration and detection of molecular biomarkers remain as a challenge to develop point-of-care diagnostic devices. An electric field induced concentration has been studied for such purposes but with limited success due to limited efficacy. This paper presents a computational study for investigating the molecular concentration and retention efficacy of single nanowire (SNW) and dendritic nanotip (DNT) sensors. Our computational results indicate that compared to a DNT, the SNW sensor produces higher dielectrophoretic (DEP) forces in the vicinity of the terminal end of the tip. Furthermore, the magnitude of the DEP force increases exponentially as the diameter of the SNW is decreased, resulting in a further improved retention efficacy of NPs. However, the SNW sensor's concentration efficacy was not much improved for NPs smaller than 10 nm diameter when the nanowire diameter was reduced from 500 to 50 nm. Compared to the SNW, the DNT sensor showed improved concentration efficacy due to multiple points of electric field concentrations, which retard the exponential decay of the DEP force resulting in a greater widespread region where the DEP force dominates the Brownian motion forces. When oligonucleotides are used as a target particle, the DEP force can be used to elongate oligonucleotides to further enhance the concentration and retention efficacy.