Recent Advancements in Receptor Layer Engineering for Applications in SPR-Based Immunodiagnostics

The rapid progress in the development of surface plasmon resonance-based immunosensing platforms offers wide application possibilities in medical diagnostics as a label-free alternative to enzyme immunoassays. The early diagnosis of diseases or metabolic changes through the detection of biomarkers in body fluids requires methods characterized by a very good sensitivity and selectivity. In the case of the SPR technique, as well as other surface-sensitive detection strategies, the quality of the transducer-immunoreceptor interphase is crucial for maintaining the analytical reliability of an assay. In this work, an overview of general approaches to the design of functional SPR-immunoassays is presented. It covers both immunosensors, the design of which utilizes well-known and often commercially available substrates, as well as the latest solutions developed in-house. Various approaches employing chemical and passive binding, affinity-based antibody immobilization, and the introduction of nanomaterial-based surfaces are discussed. The essence of their influence on the improvement of the main analytical parameters of a given immunosensor is explained. Particular attention is paid to solutions compatible with the latest trends in the development of label-free immunosensors, such as platforms dedicated to real-time monitoring in a quasi-continuous mode, the use of in situ-generated receptor layers (elimination of the regeneration step), and biosensors using recombinant and labelled protein receptors.

Electrical Control of the Receptor Affinity

A concept of virtual sensor array based on an electrically controlled variation of affinity properties of the receptor layer was realized on the base of integrated electrochemical chemotransistor containing conducting polymer as the receptor layer. Electrical control of the redox-state of the polymer (polyaniline) was performed in a five-electrode configuration with four electrodes for conductivity measurements and Ag/AgCl reference electrode integrated on the same glass chip. An ionic liquid provided an electrical connection between the reference electrode and chemosensitive material. Conductivity measurements demonstrated potential controlled electrochemical conversions of the receptor material between different redox states. The binding of trimethylamine at three different potentials corresponding to these states was studied. The results demonstrated that both kinetic- and equilibrium-binding properties of the receptor are controlled by the electrical potential, thus providing a possibility to form a virtual sensor array using only a single sensing element. The concept was applied for monitoring fish headspace. Using three characteristics of the sensor response measured at three different redox states of the same sensor material, we obtained signals from a virtual sensor array consisting of nine chemosensitive elements. The sensor displays systematic changes of its nine signals during fish degradation. This approach can be applied also for the electrical control of the affinity of immunoglobulins. Development of new materials with electrically controlled affinity is in progress.

A meta-analysis of the influence of the external conditions on the biosensor receptor layer component stability

The manuscript presented here contains meta-analysis of the influence of the external conditions on the biosensor receptor layer component stability. The novelty of this paper is due to compilation and comparison of studies, based on proposed collective analyses. The presented meta-analysis allows to increase the precision and accuracy of the results by combining and co-analyzing data from five smaller experiments. To understand the significance of presented meta-analysis, the most important conclusions and observations resulting from the conducted five types of research [F1] to [F5] are given. The conducted meta-analysis showed the magnitude of stability differences caused by different external factors. An approach of numerical interpretation of the qualitative stability changes has been offered. The conducted meta-analysis showed that the tested factors influence the stability of the BSA in different ways

Stability of the Cross Linking Component of the Biosensor Receptor Layer after Addition of Gold Nanoparticles

In this study, the stability of the receptor layer component of a biosensor after addition of gold nanoparticles was investigated. Accelerated conformational changes under the influence of Au were demonstrated. The relative percentage changes over time between the pure protein and the Au doped protein were calculated. It was shown that these changes are greater with time and exceed 20 % in the last days of the experiment.

Nanomaterial-Enhanced Receptor Technology for Silicon On-Chip Biosensing Application

Nanomaterials integration in biosensors designs are known to enhance sensing and signaling capabilities by exhibiting remarkably high surface area enhancement and intrinsic reactivity owing to their distinctive optical, chemical, electrical and catalytic properties. We present the synthesis and characterization of silver nanoparticles (AgNPs), and their immobilization on a silicon on-chip biosensor platform to enhance sensing capability for prostate specific antigen (PSA) - cancer biomarkers. Several techniques, including UV-Visible (UV-Vis) absorption spectrum, Fourier transforms infrared spectroscopy (FTIR), high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM) and field emission scanning electron microscopy (FESEM) were used for characterizing the AgNPs. The biochemical sensor consists of AgNPs immobilized on the receptor layer of a silicon avalanche mode light emitting device (Si AM LED) which enables on-chip optical detection biological analytes. A bio-interaction layer etched from the chip interacts with the evanescent field of a micro dimensioned waveguide. An array of detectors below the receptor cavity selectively monitor reflected light in the UV, visible, infrared and far infrared wavelength regions. AgNPs used as an immobilization layer in the receptor layer enhances selective absorption analytes, causing a change in detection signal as a function of propagation wavelength as light is dispersed. The analytes could range from gases to cancer biomarkers like prostate specific antigen.

Si-corrole-based fluoride fluorometric turn-on sensor

We present here a new type of fluoride ion optode, constituted by a highly lipophilic PVDF porous membrane modified with a liquid receptor layer containing the emission-active Si corrole F[Formula: see text] selective ionophore. For the optimized composition of the receptor layer, in acidic solutions an increase of Si-corrole emission was observed by increasing fluoride ion concentration, a behavior different from most porphyrinoid-based optical sensors. An observed linear dependence of the Si corrole emission intensity (read at 635 nm) was within the range 10[Formula: see text] to 10[Formula: see text] M of fluoride ions.

Finite Element Analysis of Interface Dependence on Nanomechanical Sensing

Nanomechanical sensors and their arrays have been attracting significant attention for detecting, discriminating and identifying target analytes. The sensing responses can be partially explained by the physical properties of the receptor layers coated on the sensing elements. Analytical solutions of nanomechanical sensing are available for a simple cantilever model including the physical parameters of both a cantilever and a receptor layer. These analytical solutions generally rely on the simple structures, such that the sensing element and the receptor layer are fully attached at their boundary. However, an actual interface in a real system is not always fully attached because of inhomogeneous coatings with low affinity to the sensor surface or partial detachments caused by the exposure to some analytes, especially with high concentration. Here, we study the effects of such macroscopic interfacial structures, including partial attachments/detachments, for static nanomechanical sensing, focusing on a Membrane-type Surface stress Sensor (MSS), through finite element analysis (FEA). We simulate various macroscopic interfacial structures by changing the sizes, numbers and positions of the attachments as well as the elastic properties of receptor layers (e.g., Young’s modulus and Poisson’s ratio) and evaluate the effects on the sensitivity. It is found that specific interfacial structures lead to efficient sensing responses, providing a guideline for designing the coating films as well as optimizing the interfacial structures for higher sensitivity including surface modification of the substrate.