Surface Plasmon Resonance Sensors: Methods of Surface Functionalization and Sensitivity Enhancement

Combining plasmonic and electrochemical biosensing methods

The idea of combining electrochemical (EC) and plasmonic biosensor methods was introduced almost thirty years ago and the potential of electrochemical-plasmonic (EC-P) biosensors has been highlighted ever since. Despite that, the use of EC-P biosensors in analytics has been rather limited so far and the search for unique applications of the EC-P method continues. In this paper, we review the advances in the field of EC-P biosensors and discuss the features and benefits they can provide. In addition, we identify the main challenges for the development of EC-P biosensors and the limitations that prevent EC-P biosensors from more widespread use. Finally, we review applications of EC-P biosensors for the investigation and quantification of biomolecules, and for the study of biomolecular and cellular processes.

Theoretical optimization of a frequency-domain- based color polarization interference sensor via coupling with a Gaussian beam

In this paper, a Gaussian-beam-coupled color polarization interference (CCPI) sensor with an adjustable digital Gaussian filter was proposed theoretically in the frequency domain. The coupling principle of a traditional color polarization interference (CPI) sensor and a Gaussian beam was investigated, and sensitivity optimization was then implemented. The formation of a doublet is related to the shape of a CPI curve, expected wavelength, and FWHM of the Gaussian beam. Based on the calculated results, the angle between the two polarizers and the obliquity of the wave plate are the two most significant adjusting parameters. The sensitivity of a CCPI sensor is approximately twofold higher than that of a traditional CPI sensor. The sensing range is also related to the FWHM of the Gaussian beam and a larger FWHM usually means a wider sensing range. We also found that the sensitivity would reach a maximum when the incident angle is near the total internal reflection angle. Besides, a longer incident wavelength usually corresponds to a higher sensitivity and the sensitivity could reach as high as 9270 nm/refractive index unit when the resonance wavelength is 977.40 nm.

Overview and emerging trends in optical fiber aptasensing

Optical fiber biosensors have attracted growing interest over the last decade and quickly became a key enabling technology, especially for the detection of biomarkers at extremely low concentrations and in small volumes. Among the many and recent fiber-optic sensing amenities, aptamers-based sensors have shown unequalled performances in terms of ease of production, specificity, and sensitivity. The immobilization of small and highly stable bioreceptors such as DNA has bolstered their use for the most varied applications e.g., medical diagnosis, food safety and environmental monitoring. This review highlights the recent advances in aptamer-based optical fiber biosensors. An in-depth analysis of the literature summarizes different fiber-optic structures and biochemical strategies for molecular detection and immobilization of receptors over diverse surfaces. In this review, we analyze the features offered by those sensors and discuss about the next challenges to be addressed. This overview investigates both biochemical and optical parameters, drawing the guiding lines for forthcoming innovations and prospects in this ever-growing field of research.

Strategy of Dimercaptothiol as Self-assembled Monolayers Enhance the Sensitivity of SPR Immunosensor for Detection of Salbutamol

The formation of self-assembled monolayers (SAMs) is a normal method for the immobilization of biorecognition elements immobilized on SPR sensors. With this method, mercaptopropionic acid (MPA) with carboxylic and thiol group is the most commonly used. Dimercaptosuccinic acid (DMSA) having two carboxylics and two thiol groups is a classical antidote for heavy metal ions. In this paper, DMSA was first used to form SAMs to connect the antigen on the chip of a surface plasmon resonance (SPR) immunosensor for detection of salbutamol (SAL), and the results were compared with a traditional (MPA)-SPR sensor. Dihydrolipoic acid(DHLA)-SPR showed that the recognition efficiency of antigen and antibody of DMSA-SPR immunosensor was 170.1% at room temperature with the linear range of 5 - 150 ng/mL. The recovery rate of this sensor applied to SAL detection in pork reached 94.9 - 108.0% and the limit of quantification (LOQ) was 5 ng/mL. The results were in good correlation with the analysis results of ultra-high phase liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) analysis. This novel DMSA-SPR immunosensor provides insight into a new idea and method for improving the sensitivity of SPR immunosensors and can be widely used in the detection of other small molecules.

An Impedance Based Electrochemical Immunosensor for Aflatoxin B1 Monitoring in Pistachio Matrices

Aflatoxins are highly toxic fungal secondary metabolites that often contaminate food and feed commodities. An electrochemical immunosensor for the determination of aflatoxin B1 (AFB1) was fabricated by immobilizing monoclonal AFB1 antibodies onto a screen-printed gold electrode that was modified with carbo-methyldextran by N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride/N-hydroxysuccinimide cross-linking. An electrochemical interfacial modelling of biomolecular recognition was suggested and reasonably interpreted. Impedance technology was employed for the quantitative determination of AFB1. The limit of detection concentration of AFB1 for standard solutions and spiked pistachio samples was 0.5 ng/mL and 1 ng/mL, respectively. The immunosensor was able to successfully determine AFB1 concentrations in the range of 4.56–50.86 ng/mL in unknown pistachio samples. Comparative chromatographic analysis revealed that AFB1 concentrations that were higher than 345 ng/mL were not within the immunosensor’s upper limits of detection. Selectivity studies against Ochratoxin A and Aflatoxin M1 demonstrated that the proposed AFB1 immunosensor was able to differentiate between these other fungal mycotoxins. The novel electrochemical immunosensor approach has the potential for rapid sample screening in a portable, disposable format, thus contributing to the requirement for effective prevention and the control of aflatoxin B1 in pistachios.

Oriented assembly of surface plasmon resonance biosensor through staphylococcal protein A for the chlorpyrifos detection

In this study, we report a direct surface plasmon resonance (SPR) biosensor based on an oriented assembly of antibody for the rapid detection of chlorpyrifos residue in agricultural samples. In this covalent-orientated strategy, staphylococcal protein A (SPA) was first covalently bound to the surface for monitoring chlorpyrifos residue, with subsequent binding of the antibody in an orientated fashion via its fragment crystallizable (Fc) region. Consequently, the SPA-modified biosensor exhibited a satisfactory specificity and a low detection limit of 0.056 ng mL^-1 for chlorpyrifos, with a linear detection range of 0.25-50.0 ng mL^-1. Under optimal conditions, the sensor chip could be regenerated for at least 210 cycles. The results presented here indicate that the SPA-modified sensor chip can successfully improve the sensitivity and obviating the need of the modification of the antibody. The developed SPR biosensor method has the great potential for rapid, sensitive, and specific detection with broad applications in areas of environmental monitoring and food safety. Graphical abstract.

Label-Free Graphene Oxide-Based Surface Plasmon Resonance Immunosensor for the Quantification of Galectin-3, a Novel Cardiac Biomarker

We report the first optical biosensor for the novel and important cardiac biomarker, galectin-3 (Gal3), using the anti-Gal3 antibody as a biorecognition element and surface plasmon resonance (SPR) for transducing the bioaffinity event. The immunosensing platform was built at a thiolated Au surface modified by self-assembling four bilayers of poly(diallyldimethylammonium chloride) and graphene oxide (GO), followed by the covalent attachment of 3-aminephenylboronic acid (3ABA). The importance of GO, both as the anchoring point of the antibody and as a field enhancer for improving the biosensor sensitivity, was critically discussed. The advantages of using 3ABA to orientate the anti-Gal3 antibody through the selective link to the Fc region were also demonstrated. The new platform represents an interesting alternative for the label-free biosensing of Gal3 in the whole range of clinically relevant concentrations (linear range between 10.0 and 50.0 ng mL^-1, detection limit of 2.0 ng mL^-1) with successful application for Gal3 biosensing in enriched human serum samples.