An enhanced SPR immunosensing platform for human IgG based on the use of silver nanocubes and carboxy-functionalized graphene oxide

Isothermal titration calorimetry and surface plasmon resonance methods to probe protein-protein interactions

Isothermal titration calorimetry (ITC) and surface plasmon resonance (SPR) are two commonly used methods to probe biomolecular interactions. ITC can provide information about the binding affinity, stoichiometry, changes in Gibbs free energy, enthalpy, entropy, and heat capacity upon binding. SPR can provide information about the association and dissociation kinetics, binding affinity, and stoichiometry. Both methods can determine the nature of protein-protein interactions and help understand the physicochemical principles underlying complex biochemical pathways and communication networks. This methods article discusses the practical knowledge of how to set up and troubleshoot these two experiments with some examples.

MoS2-Nanoflower and Nanodiamond Co-Engineered Surface Plasmon Resonance for Biosensing

Surface plasmon resonance (SPR) based sensors play an important role in the biological and medical fields, and improving the sensitivity is a goal that has always been pursued. In this paper, a sensitivity enhancement scheme jointly employing MoS₂ nanoflower (MNF) and nanodiamond (ND) to co-engineer the plasmonic surface was proposed and demonstrated. The scheme could be easily implemented via physically depositing MNF and ND overlayers on the gold surface of an SPR chip, and the overlayer could be flexibly adjusted by controlling the deposition times, thus approaching the optimal performance. The bulk RI sensitivity was enhanced from 9682 to 12,219 nm/RIU under the optimal condition that successively deposited MNF and ND 1 and 2 times. The proposed scheme was proved in an IgG immunoassay, where the sensitivity was twice enhanced compared to the traditional bare gold surface. Characterization and simulation results revealed that the improvement arose from the enhanced sensing field and increased antibody loading via the deposited MNF and ND overlayer. At the same time, the versatile surface property of NDs allowed a specifically-functionalized sensor using the standard method compatible with a gold surface. Besides, the application for pseudorabies virus detection in serum solution was also demonstrated.

Tunable surface plasmon resonance enhanced fluorescence via the stretching of a gold quantum dot-coated aluminum-coated elastomeric grating substrate

In this study, the surface plasmon resonance (SPR)-enhanced fluorescence properties of gold quantum dots (AuQDs) on an aluminum (Al)-coated polydimethylsiloxane (PDMS) grating substrate were investigated by changing the grating pitch via mechanical stretching. The SPR-excitation wavelength of the AuQDs/Al-coated PDMS-grating substrate was tuned by changing the incident light angle from 5° to 60° and stretching it from 0 to 1.0 mm. In addition, the SPR-enhanced fluorescence tuning ability was studied using an AuQD/Al-coated PDMS-grating film by stretching the substrate. The SPR-enhanced fluorescence (SPF) of the AuQDs on the Al-grating was observed using a violet laser as the excitation source at 405 nm with p-polarization. The wavelengths of the SPR excitation, corresponding to the SP-dispersion mode of +1, were shifted to a longer wavelength upon stretching the grating substrate from 0 to 1.0 mm. By stretching the AuQDs/Al-grating PDMS substrate, the SPR-enhanced fluorescence intensity increased at fixed incident angles of 15° and 35°, whereas the SPR-enhanced fluorescence intensity decreased at 40°. Moreover, the SPF could be tuned to exhibit different properties in tunable optical sensors.

Biotin-streptavidin sandwich integrated PDA-ZnO@Au nanocomposite based SPR sensor for hIgG detection

SPR is a mature optical biosensor technology for detecting biomolecular interactions without fluorescence or enzyme labeling. In this paper, we acquire a sensitive SPR biosensor based on ZnO@Au nanomaterial, and the classical sandwich strategy using biotin-streptavidin for secondary signal amplification system was used to detect human IgG (hIgG). Nano-zinc oxide (ZnO) has the dual characteristics of nanocomposite and traditional zinc oxide, with large specific surface area and high chemical activity. Besides, the gold-coated ZnO nanocrystals improve the optical properties of ZnO and enlarge the loading capacity with better biocompatibility. Therefore, a sensing platform based on PDA-ZnO@Au nanomaterial was constructed on gold film modified with mercaptan. Meanwhile, the biotin-avidin system in SPR sensor field has been rapidly developed and applied. Due to the highly selection of streptavidin (SA) and biotin interact with each other, GNRs-SA-biotin-Ab₂ (GSAB-Ab₂) were constructed to obtain the secondary enhancement of SPR signal. The influences of experimental conditions were also discussed. With optimal experimental conditions, introducing GSAB-Ab₂ conjugate combined with a sandwich format, the resulting SPR biosensor provides a favourable range for hIgG determination of 0.0375-40 μg mL^-1. The minimum detection concentration of hIgG that can be obtained by this method is approximately 67-fold lower than the conventional SPR sensor based on gold film. The sensitivity of SPR biosensor is significantly improved in a certain range.

Single-Layer-Graphene-Coated and Gold-Film-Based Surface Plasmon Resonance Prism Coupler Sensor for Immunoglobulin G Detection

A graphene-based surface plasmon resonance (SPR) prism coupler sensor is proposed for the rapid detection of immunoglobulin G (IgG) antibodies. The feasibility of the proposed sensor is demonstrated by measuring the IgG concentration in phantom mouse and human serum solutions over the range of 0–250 ng/mL. The results show that the circular dichroism and principal fast axis angle of linear birefringence increase in line with increases in IgG concentration over the considered range. Moreover, the proposed device has a resolution of 5–10 ng/mL and a response time of less than three minutes. In general, the sensor provides a promising approach for IgG detection and has significant potential for rapid infectious viral disease testing applications.

A Versatile Terahertz Chemical Microscope and Its Application for the Detection of Histamine

Terahertz waves have gained increasingly more attention because of their unique characteristics and great potential in a variety of fields. In this study, we introduced the recent progress of our versatile terahertz chemical microscope (TCM) in the detection of small biomolecules, ions, cancer cells, and antibody–antigen immunoassaying. We highlight the advantages of our TCM for chemical sensing and biosensing, such as label-free, high-sensitivity, rapid response, non-pretreatment, and minute amount sample consumption, compared with conventional methods. Furthermore, we demonstrated its new application in detection of allergic-related histamine at low concentration in buffer solutions.

Surface plasmon resonance prism coupler for enhanced circular birefringence sensing and application to non-invasive glucose detection

A surface plasmon resonance (SPR) prism coupler is proposed for the high-resolution non-invasive (NI) measurement of the circular birefringence (CB) properties of turbid media. The feasibility of the proposed device is demonstrated by means of numerical simulations. It is shown that the SPR sensor enables the CB properties to be detected with a resolution of up to 8.9 × 10^-7 RIU (refractive index units) for refractive indices in the range of 1.3∼1.4. Moreover, for tissue phantom solutions containing 2% lipofundin, the device has a detection limit of 3.72 mg/dL. This resolution performance satisfies the detection limit of 10 mg/dL stipulated by the U.S FDA for point-of-care glucose monitoring devices. Thus, the proposed SPR sensor has significant potential for NI glucose sensing in such applications as diabetes detection and management.

Graphene oxide-based fluorometric determination of methicillin-resistant Staphylococcus aureus by using target-triggered chain reaction and deoxyribonuclease-assisted recycling

The authors describe a method for the fluorometric determination of methicillin-resistant Staphylococcus aureus (MRSA) by exploiting target-triggered chain reactions and deoxyribonuclease I (DNase I)-aided target recycling. It is making use of a carboxy-fluorescein (FAM)-labeled single-stranded probe containing two sections. One is complementary to the 5' terminus of the target, while the 3' terminus of the other target is adsorbed on the surface of graphene oxide (GO) via π-stacking interactions without the target (16S rRNA). This adsorption results in quenching of the fluorescence of the label and protects it from being cleaved by DNase I. However, upon addition of the target, DNA/RNA hybrids are repelled by GO. This leads to fluorescence recovery as measured at excitation/emission wavelengths of 480/514 nm due to a chain reaction that is triggered by the target. The signal is strongly amplified by using DNase I-mediated target recycling. The 16S rRNA of MRSA can be detected by this method in the 1 to 30 nM concentration range, and the detection limit is 0.02 nM. The method was applied to analyze bacterial samples, and the detection limit is as low as 30 CFU . mL^-1. The assay is highly sensitive and selective and in our percpetion has a large potential in diagnosis of drug-resistant bacteria. Graphical abstract Schematic of the graphene oxide-based fluorescent bioassay for Methicillin-resistant Staphylococcus aureus detection by using target-triggered chain reaction and deoxyribonuclease I-aided signal amplification.