Light-Addressable Actuator-Sensor Platform for Monitoring and Manipulation of pH Gradients in Microfluidics: A Case Study with the Enzyme Penicillinase

Light Addressable Potentiometric Sensors for Biochemical Imaging on Microscale: A Review on Optimization of Imaging Speed and Spatial Resolution

Light addressable potentiometric sensors (LAPS) are a competitive tool for unmarked biochemical imaging, especially imaging on microscale. It is essential to optimize the imaging speed and spatial resolution of LAPS since the imaging targets of LAPS, such as cell, microfluidic channel, etc., require LAPS to image at the micrometer level, and a fast enough imaging speed is a prerequisite for the dynamic process involved in biochemical imaging. In this study, we discuss the improvement of LAPS in terms of imaging speed and spatial resolution. The development of LAPS in imaging speed and spatial resolution is demonstrated by the latest applications of biochemistry monitoring and imaging on the microscale.

Facile Purification and Use of Tobamoviral Nanocarriers for Antibody-Mediated Display of a Two-Enzyme System

Immunosorbent turnip vein clearing virus (TVCV) particles displaying the IgG-binding domains D and E of Staphylococcus aureus protein A (PA) on every coat protein (CP) subunit (TVCVPA) were purified from plants via optimized and new protocols. The latter used polyethylene glycol (PEG) raw precipitates, from which virions were selectively re-solubilized in reverse PEG concentration gradients. This procedure improved the integrity of both TVCVPA and the wild-type subgroup 3 tobamovirus. TVCVPA could be loaded with more than 500 IgGs per virion, which mediated the immunocapture of fluorescent dyes, GFP, and active enzymes. Bi-enzyme ensembles of cooperating glucose oxidase and horseradish peroxidase were tethered together on the TVCVPA carriers via a single antibody type, with one enzyme conjugated chemically to its Fc region, and the other one bound as a target, yielding synthetic multi-enzyme complexes. In microtiter plates, the TVCVPA-displayed sugar-sensing system possessed a considerably increased reusability upon repeated testing, compared to the IgG-bound enzyme pair in the absence of the virus. A high coverage of the viral adapters was also achieved on Ta2O5 sensor chip surfaces coated with a polyelectrolyte interlayer, as a prerequisite for durable TVCVPA-assisted electrochemical biosensing via modularly IgG-assembled sensor enzymes.

A surface plasmon resonance sensor with synthetic receptors decorated on graphene oxide for selective detection of benzylpenicillin

Antibiotic residues in foods, water and the environment reveal antibiotic-resistant bacterial strains, disrupting the ecological balance and causing serious health problems. For these reasons, the detection of antibiotic residues is crucial for the protection of human health. Herein, the detection of benzylpenicillin antibiotic from aqueous and milk sample solutions was carried out by surface plasmon resonance (SPR) sensor using synthetic receptor-molecularly imprinted polymer. The benzylpenicillin-imprinted poly(hydroxyethyl methacrylate-graphene oxide-N-methacryloyl-l-phenylalanine) (MIP-GO) SPR sensor was prepared. Benzylpenicillin detection was performed by MIP-GO SPR sensor in a 1-100 ppb concentration range of benzylpenicillin with 0.9665 linear correlation and 0.021 ppb detection limit. Selectivity analysis showed that the MIP-GO SPR sensor detected the benzylpenicillin molecule 8.16 times more selectively than amoxicillin and 14.04 times more selectively than ampicillin. To examine the imprinting efficiency, non-imprinted poly(hydroxyethyl methacrylate-graphene oxide-N-methacryloyl-l-phenylalanine) (NIP-GO) SPR sensor was also prepared using the same procedure without benzylpenicillin addition. Since graphene oxide (GO) was added to enhance the sensor signal response by increasing sensitivity, the control analyses were performed by a poly(hydroxyethyl methacrylate-N-methacryloyl-l-phenylalanine) (MIP) SPR sensor without adding GO. Moreover, repeatability studies of MIP-GO SPR sensor were statistically evaluated and the RSD of intra-day assays less than 1% specified that there was no loss of performance for the benzylpenicillin detection ability even after four cycles. As a real food sample analysis, the benzylpenicillin spiked and unspiked milk samples were evaluated and high-performance liquid chromatography experiments were carried out for validation.

Convenient site-selective protein coupling from bacterial raw lysates to coenzyme A-modified tobacco mosaic virus (TMV) by Bacillus subtilis Sfp phosphopantetheinyl transferase

A facile enzyme-mediated strategy enables site-specific covalent one-step coupling of genetically tagged luciferase molecules to coenzyme A-modified tobacco mosaic virus (TMV-CoA) both in solution and on solid supports. Bacillus subtilis surfactin phosphopantetheinyl transferase Sfp produced in E. coli mediated the conjugation of firefly luciferase N-terminally extended by eleven amino acids forming a 'ybbR tag' as Sfp-selective substrate, which even worked in bacterial raw lysates. The enzymes displayed on the protein coat of the TMV nanocarriers exhibited high activity. As TMV has proven a beneficial high surface-area adapter template stabilizing enzymes in different biosensing layouts in recent years, the use of TMV-CoA for fishing ybbR-tagged proteins from complex mixtures might become an advantageous concept for the versatile equipment of miniaturized devices with biologically active proteins. It comes along with new opportunities for immobilizing multiple functionalities on TMV adapter coatings, as desired, e.g., in handheld systems for point-of-care detection.

Light-Addressable Electrochemical Sensors toward Spatially Resolved Biosensing and Imaging Applications

The light-addressable electrochemical sensor (LAES) is a recently emerged bioanalysis technique combining electrochemistry with the photoelectric effect in a semiconductor. In an LAES, a semiconductor substrate is illuminated locally to generate charge carriers in a well-defined area, thereby confining the electrochemical process to a target site. Benefiting from the unique light addressability, an LAES can not only detect multiple analytes in parallel within a single sensor plate but also act as a bio(chemical) imaging sensor to visualize the two-dimensional distribution of specific analytes. An LAES usually has three working modes: a potentiometric mode using light-addressable potentiometric sensors (LAPS) and an impedance mode using scanning photoinduced impedance microscopy (SPIM), while an amperometric mode refers to light-addressable electrochemistry (LAE) and photoelectrochemical (PEC) sensing. In this review, we describe the detection principles of each mode of LAESs and the concept of light addressability. In addition, we highlight the recent progress and advance of LAESs in spatial resolution, sensor system design, multiplexed detection, and bio(chemical) imaging applications. An outlook on current research challenges and future prospects is also presented.

Detection of Acetoin and Diacetyl by a Tobacco Mosaic Virus-Assisted Field-Effect Biosensor

Acetoin and diacetyl have a major impact on the flavor of alcoholic beverages such as wine or beer. Therefore, their measurement is important during the fermentation process. Until now, gas chromatographic techniques have typically been applied; however, these require expensive laboratory equipment and trained staff, and do not allow for online monitoring. In this work, a capacitive electrolyte–insulator–semiconductor sensor modified with tobacco mosaic virus (TMV) particles as enzyme nanocarriers for the detection of acetoin and diacetyl is presented. The enzyme acetoin reductase from Alkalihalobacillus clausii DSM 8716T is immobilized via biotin–streptavidin affinity, binding to the surface of the TMV particles. The TMV-assisted biosensor is electrochemically characterized by means of leakage–current, capacitance–voltage, and constant capacitance measurements. In this paper, the novel biosensor is studied regarding its sensitivity and long-term stability in buffer solution. Moreover, the TMV-assisted capacitive field-effect sensor is applied for the detection of diacetyl for the first time. The measurement of acetoin and diacetyl with the same sensor setup is demonstrated. Finally, the successive detection of acetoin and diacetyl in buffer and in diluted beer is studied by tuning the sensitivity of the biosensor using the pH value of the measurement solution.

Light-Addressable Potentiometric Sensors in Microfluidics

The light-addressable potentiometric sensor (LAPS) is an electrochemical sensor based on the field-effect principle of semiconductors. It is able to sense the change of Nernst potential on the sensor surface, and the measuring area can be controlled by the illumination of a movable light. Due to the unique light-addressable ability of the LAPS, the chemical imaging system constructed with the LAPS can realize the two-dimensional image distribution detection of chemical/biomass. In this review, the advantages of the LAPS as a sensing unit of the microelectrochemical analysis system are summarized. Then, the most recent advances in the development of the LAPS analysis system are explained and discussed. In particular, this review focused on the research of ion diffusion, enzymatic reaction, microbial metabolism, and droplet microfluidics using the LAPS analysis system. Finally, the development trends and prospects of the LAPS analysis system are illustrated.

Towards Multi-Analyte Detection with Field-Effect Capacitors Modified with Tobacco Mosaic Virus Bioparticles as Enzyme Nanocarriers

Utilizing an appropriate enzyme immobilization strategy is crucial for designing enzyme-based biosensors. Plant virus-like particles represent ideal nanoscaffolds for an extremely dense and precise immobilization of enzymes, due to their regular shape, high surface-to-volume ratio and high density of surface binding sites. In the present work, tobacco mosaic virus (TMV) particles were applied for the co-immobilization of penicillinase and urease onto the gate surface of a field-effect electrolyte-insulator-semiconductor capacitor (EISCAP) with a p-Si-SiO₂-Ta₂O₅ layer structure for the sequential detection of penicillin and urea. The TMV-assisted bi-enzyme EISCAP biosensor exhibited a high urea and penicillin sensitivity of 54 and 85 mV/dec, respectively, in the concentration range of 0.1-3 mM. For comparison, the characteristics of single-enzyme EISCAP biosensors modified with TMV particles immobilized with either penicillinase or urease were also investigated. The surface morphology of the TMV-modified Ta₂O₅-gate was analyzed by scanning electron microscopy. Additionally, the bi-enzyme EISCAP was applied to mimic an XOR (Exclusive OR) enzyme logic gate.

Selective Detection of Penicillin G Antibiotic in Milk by Molecularly Imprinted Polymer-Based Plasmonic SPR Sensor

Molecularly imprinted polymer-based surface plasmon resonance sensor prepared using silver nanoparticles was designed for the selective recognition of Penicillin G (PEN-G) antibiotic from both aqueous solution and milk sample. PEN-G imprinted sensors (NpMIPs) SPR sensor was fabricated using poly (2-hydroxyethyl methacrylate-N-methacroyl-(L)-cysteine methyl ester)-silver nanoparticles-N-methacryloyl-L-phenylalanine methyl ester polymer by embedding silver nanoparticles (AgNPs) into the polymeric film structure. In addition, a non-imprinted (NpNIPs) SPR sensor was prepared by utilizing the same polymerization recipe without addition of the PEN-G template molecule to evaluate the imprinting effect. FTIR-ATR spectrophotometer, ellipsometer, contact angle measurements were used for the characterization of NpMIPs SPR sensors. The linear concentration range of 0.01–10 ng/mL PEN-G was studied for kinetic analyses. The augmenting effect of AgNPs used to increase the surface plasmon resonance signal response was examined using polymer-based PEN-G imprinted (MIPs) sensor without the addition of AgNPs. The antibiotic amount present in milk chosen as a real sample was measured by spiking PEN-G into the milk. According to the Scatchard, Langmuir, Freundlich and Langmuir–Freundlich adsorption models, the interaction mechanism was estimated to be compatible with the Langmuir model.