Target-triggering multiple-cycle signal amplification strategy for ultrasensitive detection of DNA based on QCM and SPR

Development of a surface plasmon resonance (SPR) assay for rapid detection of Aeromonas hydrophila

Aquaculture plays an increasingly important if not critical role in the current and future world food supply. Aeromonas hydrophila, a heterotrophic, Gram-negative, bacterium found in fresh or brackish water in warm climates poses a serious threat to the aquaculture industry in many areas, causing significant economic losses. Rapid, portable detection methods of A. hydrophila are needed for its effective control and mitigation. We have developed a surface plasmon resonance (SPR) technique to detect PCR (polymerase chain reaction) products that can replace agarose gel electrophoresis, or otherwise provide an alternative to costlier and more complicated real-time, fluorescence-based detection. The SPR method provides sensitivity comparable to gel electrophoresis, while reducing labor, cross-contamination, and test time, and employs simpler instrumentation with lower cost than real-time PCR.

Research on Tunable SPR Sensors Based on WS2 and Graphene Hybrid Nanosheets

A prismatic excitation-based affinity biosensor consisting of the prism (BK7), WS2/graphene hybrid nanosheets, and silver (Ag) as the active metal for the surface plasmon resonance is proposed in this present research. The introduction of the transition metal WS2/graphene layer protected the silver substrate and enhanced the adsorption of biomolecules, which facilitated the quality and performance of detection. Here, we improved the detection structure by focusing on the metallic materials, graphene and WS2 film layers, and the thickness of the measured medium on the sensing effect. The results show that the silver film had a more desirable resonance effect, and the design of the symmetric detection structure produced a double resonance peak, and it provides a reference for distributed sensing. Changing the thickness of the detection medium can dynamically adjust the wave vector matching conditions, which gives the sensor a certain tunability. In the bilayer WS2 and monolayer graphene (W = 2, G = 1) configuration, the sensitivity was up to 224 deg/RIU with a quality factor of 96.97 RIU−1, which has potential for clinical analytic and biochemical detecting applications.

Overview of Quartz Crystal Microbalance Behavior Analysis and Measurement

Quartz Crystal Microbalance (QCM) is one of the many acoustic transducers. It is the most popular and widely used acoustic transducer for sensor applications. It has found wide applications in chemical and biosensing fields owing to its high sensitivity, robustness, small sized-design, and ease of integration with electronic measurement systems. However, it is necessary to coat QCM with a sensing film. Without coating materials, its selectivity and sensitivity are not obtained. At present, this is not an issue, mainly due to the advancement of oscillator circuits and dedicated measurement circuits. Since a new researcher may seek to understand QCM sensors, we provide an overview of QCM from its fundamental knowledge. Then, we explain some of the recent QCM applications both in gas-phase and liquid-phase. Next, the theory of QCM is introduced by using piezoelectric stress equations and the Mason equivalent circuit, which explains how the QCM behavior is obtained. Then, the conventional equations that govern QCM behaviors in terms of resonant frequency and resistance are described. We show the behavior of QCM with a viscous film based on the acoustic wave equation and Mason equivalent circuit. Then, we present various existing QCM electronic measurement methods. Furthermore, we describe the experiment on QCM with viscous loading and its interpretation based on the Mason equivalent circuit. Lastly, we review some theoretical models to describe QCM behavior with various models.

Optimization Based on the Surface Plasmon Optical Properties of Adjustable Metal Nano-Microcavity System for Biosensing

This paper mainly studies the plasma optical properties of the silver nanorod and gold film system with gap structure. During the experiment, the finite element analysis method and COMSOL Multiphysics are used for modeling and simulation. The study changes the thickness of the PE spacer layer between the silver nanorod and the gold film, the conditions of the incident light and the surrounding environment medium. Due to the anisotropic characteristics of silver nanorod, the microcavity system is extremely sensitive to the changes of internal and external conditions, and the system exhibits strong performance along the long axis of the nanorod. By analyzing the extinction spectrum of the nanoparticle and the electric field section diagrams at resonance peak, it is found that the plasma optical properties of the system greatly depend on the gap distance, and the surrounding electric field of the silver nanorod is confined in the gap. Both ends of the nanorod and the gap are distributed with high concentrations of hot spots, which reflects the strong hybridization of multiple resonance modes. Under certain excitation conditions, the plasma hybridization behavior will produce a multi-pole mode, and the surface electric field distribution of the nanorod reflects the spatial directionality. In addition, the system is also highly sensitive to the environmental media, which will cause significant changes in its optical properties. The plasma microcavity system with silver nanorod and gold film studied in this paper can be used to develop high-sensitivity biosensors, which has great value in the field of biomedical detection.

Surface plasmon resonance biosensor for the detection of miRNAs by combining the advantages of homogeneous reaction and heterogeneous detection

The hybridization and enzymolysis reactions for nucleic acid detection were carried out on the chip surface in the traditional surface plasmon resonance (SPR) biosensors. Herein, we proposed an innovative method for microRNA (miRNA) detection in which the hybridization-enzymolysis recycling reactions were performed in solution. Duplex-specific nuclease (DSN) and streptavidin-modified gold nanoparticles (SA-AuNPs) were employed for enhancing the assay sensitivity. In the absence of miRNA, the biotinylated DNA probe (bio-DNA-bio, biotin tags at both the 3' and 5' termini of DNA) was attached to the SA-modified chip through the SA-biotin binding, allowing the capture of SA-AuNPs with the same interaction. As a result, a larger SPR signal was attained. However, in the presence of miRNA, bio-DNA-bio hybridized with miRNA was digested by DSN. In this process, the miRNA strand remained intact and participated in the next hybridization-enzymolysis recycling process. Thus, one miRNA could promote the hydrolysis of many bio-DNA-bio probes and allow the generation of numerous bio-DNA fragments. Meanwhile, the produced bio-DNA competed with the undigested bio-DNA-bio to bind SA on the chip surface. The digestion of bio-DNA-bio and the competitive binding between bio-DNA-bio and bio-DNA led to the attachment of fewer SA-AuNPs and then smaller SPR signals. The change in SPR signal at the concentration as low as 1 fM miRNA has been readily determined. The strategy possessed the advantageous properties of simple operation, fast response, high sensitivity and excellent specificity, serving as a viable means for the fabrication of novel sensing platforms.

Recent applications of QCM-D for the design, synthesis, and characterization of bioactive materials

The clinical translation of bioactive technologies is lacking compared to the number of novel technologies reported in the literature. This is in part due to the difficulties in characterizing bioactive materials to understand and predict their biological response. To progress the field and increase clinical success, more robust analytical techniques must be utilized when investigating novel bioactive materials. The quartz crystal microbalance with dissipation (QCM-D), a label-free sensing instrument based on an acoustic resonator, is used to quantify mass change and viscoelastic parameters from soft materials at the nanoscale, in situ, with precise temporal resolution and operation in both liquid and gaseous environments. The versatility of QCM-D has enhanced the characterization of bioactive polymers and sensing arrays for advanced applications of novel biotechnologies. In this review, we highlight exciting, recent applications of QCM-D for the investigation of bioactive materials. Attention is given to the dynamic mechanical properties of bioactive materials, discerning protein structure on surfaces, probing cell adhesion and cytoskeletal changes, and biosensing applications. We conclude that QCM-D has untapped utility in the pre-clinical investigation of bioactive materials and further utilization can improve the clinical success of novel technologies.

QCM sensing of miR-21 by formation of microRNA-DNA hybrid duplexes and intercalation on surface-functionalized pyrene

MicroRNAs (miRNAs) are small non-coding RNA molecules that serve as important biomarkers for a variety of diseases such as cancer and vascular disease. However, sensitive and accurate detection of miR-21 is very challenging in that up-regulation of miR-21 is highly associated with several types of malignant tumors. Here, quartz crystal microbalance (QCM) biosensors were developed for sensitive and specific detection of miR-21 through formation of miR-21-DNA hybrid duplexes and non-specific intercalation of surface-modified pyrene molecules. High selectivity for miR-21 over other miRNAs came from the specific hybridization between miR-21 and gold nanoparticle (AuNP)-conjugated complementary oligonucleotides of miR-21. High sensitivity was obtained through formation of intercalated complexes on the surface with subsequent gold staining signal amplification. Under optimum condition using this strategic approach, our novel QCM biosensors could detect miR-21 concentration as low as 3.6 pM in the entire linear range from 2.5 pM to 2.5 μM with a correlation coefficient of 0.989. In addition, these sensors did not work at all for other miRNAs based on their high selectivity. miR-21 in human brain total RNA and total RNA extracted from A549 cell line could also be successfully detected. Therefore, miRNA detection technology using QCM biosensors and their detection mechanisms have potential as alternatives in biological studies and clinical diagnosis.

Applications of Gold Nanoparticles in Non-Optical Biosensors

Due to their unique properties, such as good biocompatibility, excellent conductivity, effective catalysis, high density, and high surface-to-volume ratio, gold nanoparticles (AuNPs) are widely used in the field of bioassay. Mainly, AuNPs used in optical biosensors have been described in some reviews. In this review, we highlight recent advances in AuNP-based non-optical bioassays, including piezoelectric biosensor, electrochemical biosensor, and inductively coupled plasma mass spectrometry (ICP-MS) bio-detection. Some representative examples are presented to illustrate the effect of AuNPs in non-optical bioassay and the mechanisms of AuNPs in improving detection performances are described. Finally, the review summarizes the future prospects of AuNPs in non-optical biosensors.