Detection of adrenaline on poly(3-aminobenzylamine) ultrathin film by electrochemical-surface plasmon resonance spectroscopy

Recent advancements of smartphone-based sensing technology for diagnosis, food safety analysis, and environmental monitoring

The emergence of computationally powerful smartphones, relatively affordable high-resolution camera, drones, and robotic sensors have ushered in a new age of advanced sensible monitoring tools. The present review article investigates the burgeoning smartphone-based sensing paradigms, including surface plasmon resonance (SPR) biosensors, electrochemical biosensors, colorimetric biosensors, and other innovations for modern healthcare. Despite the significant advancements, there are still scarcity of commercially available smart biosensors and hence need to accelerate the rates of technology transfer, application, and user acceptability. The application/necessity of smartphone-based biosensors for Point of Care (POC) testing, such as prognosis, self-diagnosis, monitoring, and treatment selection, have brought remarkable innovations which eventually eliminate sample transportation, sample processing time, and result in rapid findings. Additionally, it articulates recent advances in various smartphone-based multiplexed bio sensors as affordable and portable sensing platforms for point-of-care devices, together with statistics for point-of-care health monitoring and their prospective commercial viability.

A Highly Electrostrictive Salt Cocrystal and the Piezoelectric Nanogenerator Application of Its 3D-Printed Polymer Composite

Ionic cocrystals with hydrogen bonding can form exciting materials with enhanced optical and electronic properties. We present a highly moisture-stable ammonium salt cocrystal [CH3C6H4CH(CH3)NH2][CH3C6H4CH(CH3)NH3][PF6] ((p-TEA)(p-TEAH)·PF6) crystallizing in the polar monoclinic C2 space group. The asymmetry in (p-TEA)(p-TEAH)·PF6 was induced by its chiral substituents, while the polar order and structural stability were achieved by using the octahedral PF6- anion and the consequent formation of salt cocrystal. The ferroelectric properties of (p-TEA)(p-TEAH)·PF6 were confirmed through P-E loop measurements. Piezoresponse force microscopy (PFM) enabled the visualization of its domain structure with characteristic "butterfly" and hysteresis loops associated with ferro- and piezoelectric properties. Notably, (p-TEA)(p-TEAH)·PF6 exhibits a large electrostrictive coefficient (Q33) value of 2.02 m4 C-2, higher than those found for ceramic-based materials and comparable to that of polyvinylidene difluoride. Furthermore, the composite films of (p-TEA)(p-TEAH)·PF6 with polycaprolactone (PCL) polymer and its gyroid-shaped 3D-printed composite scaled-up device, 3DP-Gy, were prepared and evaluated for piezoelectric energy-harvesting functionality. A high output voltage of 22.8 V and a power density of 118.5 μW cm-3 have been recorded for the 3DP-Gy device. Remarkably, no loss in voltage outputs was observed for the (p-TEA)(p-TEAH)·PF6 devices even after exposure to 99% relative humidity, showcasing their utility under extremely humid conditions.

Thiazole-Based Silver Ion Sensor for Sequential Colorimetric Visualization of Epinephrine in the Brain Tissues of an Alzheimer's Disease Model of Mouse

A thiazole-based probe, N'-((2-aminothiazol-5-yl)methylene)benzohydrazide (TBH), has been efficiently synthesized and characterized for the selective and sensitive detection of the neurotransmitter epinephrine (EP). The sensing strategy is based on the use of TBH for sequential colorimetric sensing of Ag+ and EP via in situ formation of Ag nanoparticles (Ag NPs) from the TBH-Ag+ complex. The generated Ag NPs lead to a bathochromic shift in absorption maximum and a change in color of the solution from light brown to reddish brown. TBH-Ag+ shows remarkable selectivity toward EP versus other drugs, common cations, anions, and some biomolecules. Moreover, TBH-Ag+ has a low detection limit for EP at 1.2 nM. The coordination of TBH-Ag+ has been proposed based on Job's plot, Fourier transform infrared spectroscopy (FT-IR), high-resolution mass spectrometry (HRMS), 1H NMR titration, X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray analysis (EDAX), and density functional theory (DFT) studies. The composition and morphology of the generated Ag NPs have been analyzed by XPS, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and dynamic light scattering (DLS). The proposed sensing mechanism for EP has been supported by XPS of Ag after the reaction. Further, the sensitivity of TBH-Ag+ toward EP in brain tissues of an Alzheimer's disease model of mouse has been evaluated. A thorough comparison was done for evaluation of the proposed method.

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.

Functional Group-Assisted Fluorescence Sensing Platform for Nanomolar-Level Detection of an Antineoplastic Drug and a Neurotransmitter from Environmental Water and Human Biofluids

A fast, sensitive, selective, and biocompatible dual sensor of an antineoplastic medication (methotrexate) and a neurotransmitter (adrenaline) is still being searched by present-day scientists. To overcome this issue, we have designed a functionalized, robust, bio-friendly luminescent MOF for the sensitive, selective, and rapid monitoring of methotrexate and adrenaline. This probe is the first ever reported MOF-based fluorescence sensor of methotrexate and second only for adrenaline. This fluorescence probe has a very low limit of detection (LOD) of 0.34 and 11.2 nM for adrenaline and methotrexate, respectively. The sensor can detect both the targeted analytes rapidly within 5 s. It can also detect adrenaline and methotrexate from human blood serum and urine accurately and precisely. This reusable sensor is equally efficient in detecting methotrexate from environmental water specimens. Biocompatible, user-friendly, and inexpensive chitosan@MOF@cotton composites were fabricated for the detection of adrenaline and methotrexate from the nanomolar to the micromolar range by the naked eye under a fluorescence lamp. This probe displayed high reproducibility, precision, and accuracy in sensing methotrexate and adrenaline. Fluorescence resonance energy transfer (FRET) and the inner filter effect (IFE) are the possible mechanisms for adrenaline and methotrexate sensing, respectively. The possible mechanism was supported by using required instrumental techniques and theoretical simulations.

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.

Electrochemical Dopamine Biosensor Based on Poly(3-aminobenzylamine) Layer-by-Layer Self-Assembled Multilayer Thin Film

Dopamine (DA) is an important neurotransmitter which indicates the risk of several neurological diseases. The selective determination with low detection limit is necessary for early diagnosis and prevention of neurological diseases associated with abnormal concentration of DA. The purpose of this study is to fabricate a poly(3-aminobenzylamine)/poly(sodium 4-styrenesulfonate) (PABA/PSS) multilayer thin film for use as an electrochemical DA biosensor. The PABA was firstly synthesized using a chemical oxidation method of 3-aminobenzylamine (ABA) monomer with ammonium persulfate (APS) as an oxidant. For electrochemical biosensor, the PABA/PSS thin film was fabricated on fluorine doped tin oxide (FTO)-coated glass substrate using the layer-by-layer (LBL) self-assembly method. The optimized number of bilayers was achieved using SEM and cyclic voltammetry (CV) results. The electroactivity of the optimized LBL thin film toward detection of DA in neutral solution was studied by CV and amperometry. The PABA/PSS thin film showed good sensitivity for DA sensing with sensitivity of 6.922 nA·cm-2·µM-1 and linear range of 0.1-1.0 µM (R2 = 0.9934), with low detection limit of 0.0628 µM, long-term stability and good reproducibility. In addition, the selectivity of the PABA/PSS thin film for detection of DA under the common interferences (i.e., ascorbic acid, uric acid and glucose) was also presented. The prepared PABA/PSS thin film showed the powerful efficiency for future use as DA biosensor in real sample analysis.

High-sensitivity detection of dopamine by biomimetic nanofluidic diodes derivatized with poly(3-aminobenzylamine)

During the last few years, much scientific effort has been devoted to the control of ionic transport properties of solid state nanochannels and the rational integration of chemical systems to induce changes in the ionic transport by interaction with selected target molecules for (bio)sensing purposes. In this work, we present the construction and functional evaluation of a highly sensitive dopamine-responsive iontronic device by functionalization of bullet-shaped track-etched single nanochannels in PET membranes with poly(3-aminobenzylamine) (PABA). The variety of basic groups in this amino-appended polyaniline derivative allows programming of the ion selectivity of the channel by setting the pH conditions. On the other hand, the amino-pendant groups of PABA become suitable binding sites for the selective chemical reaction with dopamine, leading to a change in the nanochannel surface charge. Thus, the exposure of the PABA-modified nanochannel to dopamine solutions selectively produces changes in the iontronic response. By rationally selecting the conditions for both the dopamine binding step and the iontronic reading, we obtained a correlation between the rectification efficiency and dopamine concentration down to the nanomolar range, which was also successfully interpreted in terms of a simple binding model.

A sensitive electrochemical immunosensor based on poly(2-aminobenzylamine) film modified screen-printed carbon electrode for label-free detection of human immunoglobulin G

This work focuses on fabricating poly(2-aminobenzylamine)-modified screen-printed carbon electrode as an electrochemical immunosensor for the label-free detection of human immunoglobulin G. To selectively detect immunoglobulin G, the anti-immunoglobulin G antibody with high affinity to immunoglobulin G was covalently linked with the amine group of poly(2-aminobenzylamine) film-deposited screen-printed carbon electrode. The selectivity for immunoglobulin G was subsequently assured by being challenged with redox-active interferences and adventitious adsorption did not significantly interfere the analyte signal. To obviate the use of costly secondary antibody, the [Fe(CN)₆]^4-/3- redox probe was instead applied to measure the number of human immunoglobulin G through the immunocomplex formation that is quantitatively related to the level of the differential pulse voltammetric current. The resulting immunosensor exhibited good sensitivity with the detection limit of 0.15 ng mL^-1, limit of quantitation of 0.50 ng mL^-1 and the linear range from 1.0 to 50 ng mL^-1. Given those striking analytical performances and the affordability arising from using cheap screen-printed carbon electrode with label-free detection, the immunosensor serves as a promising model for the next-step development of a diagnostic tool.

Application of Long-Range Surface Plasmon Resonance for ABO Blood Typing

In this study, we demonstrate a long-range surface plasmon resonance (LR-SPR) biosensor for the detection of whole cell by captured antigens A and B on the surface of red blood cells (RBCs) as a model. The LR-SPR sensor chip consists of high-refractive index glass, a Cytop film layer, and a thin gold (Au) film, which makes the evanescent field intensity and the penetration depth longer than conventional SPR. Therefore, the LR-SPR biosensor has improved capability for detecting large analytes, such as RBCs. The antibodies specific to blood group A and group B (Anti-A and Anti-B) are covalently immobilized on a grafting self-assembled monolayer (SAM)/Au surface on the biosensor. For blood typing, RBC samples can be detected by the LR-SPR biosensor through a change in the refractive index. We determined that the results of blood typing using the LR-SPR biosensor are consistent with the results obtained from the agglutination test. We obtained the lowest detection limits of 1.58 × 10⁵ cells/ml for RBC-A and 3.83 × 10⁵ cells/ml for RBC-B, indicating that the LR-SPR chip has a higher sensitivity than conventional SPR biosensors (3.3 × 10⁸ cells/ml). The surface of the biosensor can be efficiently regenerated using 20 mM NaOH. In summary, as the LR-SPR technique is sensitive and has a simple experimental setup, it can easily be applied for ABO blood group typing.

Ultra-sensitive determination of epinephrine based on TiO2-Au nanoclusters supported on reduced graphene oxide and carbon nanotube hybrid nanocomposites

A highly efficient and sensitive electrochemical sensor for EP based on reduced graphene and multi-walled carbon nanotube hybrid nanocomposites loaded TiO2-Au nano-clusters modified glassy carbon electrode was developed. The surface nature and morphology of the nanocomposite film and the electrochemical properties of the sensor were characterized by Raman spectra, X-ray powder diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectra (EDX), Fourier transform infrared spectroscopy (FT-IR), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV), respectively. Carbon nanomaterials were widely used in sensing due to its large electroactive surface area, fast electron transport and strong adsorption capacity. Meanwhile, TiO2-Au nano-clusters could accelerate the electron transfer, increase reactive site and extend electrochemical response window. The nanocomposite film could greatly enhance the response sensitivity and decrease the overpotential. The resulting sensor showed an excellent electrocatalytic activity toward EP. Under the optimum conditions (i.e. pH6.0, 0.1M PBS, preconcentration for 110s), Differential pulse voltammetry was employed to detect ultra-trace amounts of EP. The result of a wide linear range of 1.0-300nM and limited of detection 0.34nM (S/N=3) were obtained. The constructed sensor exhibited excellent accuracy and precision, the relative standard deviation (RSD) was less than 5%. The nanocomposite film sensor was successfully used to accurately detect the content of EP in practical samples, and the recoveries for the standards added are 97%-105%.

In situ electrochemical-transmission surface plasmon resonance spectroscopy for poly(pyrrole-3-carboxylic acid) thin-film-based biosensor applications

In this study, we describe the combination of transmission surface plasmon resonance (TSPR) and electrochemical techniques for the application to biosensors with conducting polymers. Electropolymerization was employed to construct poly(pyrrole-3-carboxylic acid) (PP3C) film on a gold-coated grating substrate using pyrrole-3-carboxylic acid (P3C) monomer solution in 0.5 M H(2)SO(4). In situ electrochemical-transmission surface plasmon resonance (EC-TSPR) measurements were carried out to study the kinetic and electroactivity properties of PP3C film. Immobilization of antihuman IgG on the activated surface and the binding process of human IgG and antihuman IgG in neutral solution could be detected in situ by EC-TSPR measurement. The surface modification steps on the PP3C layer led to an increase in intensity of the transmission peak. The performance, sensitivity, and utility of EC-TSPR spectroscopy showed obvious advantages for the detection of binding process with the simple experimental setup, and could be applied to the study of biomolecular interactions in various systems.