Fluorescent protein-based biosensors and their clinical applications. Prog Mol Biol Transl Sci. 2013;113:313-348. [PMID: 23244794 DOI: 10.1016/B978-0-12-386932-6.00008-9]

The role of nitric oxide in ocular surface physiology and pathophysiology

Nitric oxide (NO) has a wide array of biological functions including the regulation of vascular tone, neurotransmission, immunomodulation, stimulation of proinflammatory cytokine expression and antimicrobial action. These functions may depend on the type of isoform that is responsible for the synthesis of NO. NO is found in various ocular tissues playing a pivotal role in physiological mechanisms, namely regulating vascular tone in the uvea, retinal blood circulation, aqueous humor dynamics, neurotransmission and phototransduction in retinal layers. Unregulated production of NO in ocular tissues may result in production of toxic superoxide free radicals that participate in ocular diseases such as endotoxin-induced uveitis, ischemic proliferative retinopathy and neurotoxicity of optic nerve head in glaucoma. However, the role of NO on the ocular surface in mediating physiology and pathophysiological processes is not fully understood. Moreover, methods used to measure levels of NO in the biological samples of the ocular surface are not well established due to its rapid oxidation. The purpose of this review is to highlight the role of NO in the physiology and pathophysiology of ocular surface and propose suitable techniques to measure NO levels in ocular surface tissues and tears. This will improve the understanding of NO's role in ocular surface biology and the development of new NO-based therapies to treat various ocular surface diseases. Further, this review summarizes the biochemistry underpinning NO's antimicrobial action.

Detection of MOG-IgG by cell-based assay: moving from discovery to clinical practice

Myelin oligodendrocyte glycoprotein (MOG) is a unique CNS-specific mammalian protein that is expressed on the surface of compact myelin and oligodendrocyte cell bodies. MOG is an accessible target for autoantibodies, associated with immune-mediated demyelination in the central nervous system. The identification of MOG reactive immunoglobulin G antibodies (MOG-IgG) helps to distinguish a subgroup of patients from multiple sclerosis and other CNS disorders, reducing the risk of clinical misdiagnosis. The development of the cell-based assays (CBA) improved the detection of clinically meaningful MOG-IgG binding to conformational MOG expressed in the cell membrane surface. In this review, we describe factors that impact on the results of CBA, such as MOG conformation, protein glycosylation, addition of fluorescent tags, serum dilution, secondary antibodies, and data interpretation.

Genetically encoded biosensors for the detection of rapamycin: toward the screening of agonists and antagonists

Biosensors are valuable tools for the rapid screening of biological targets with high sensitivity and specificity. It is important to screen biological events in their native context for pharmacological and toxicological applications. However, in vitro biosensors often require purified probes and targets for screening, thus providing limited information on the biological activities of targets in their native environment. To address this issue, we developed a cell-based sensing system that could detect a biologically active small molecule, rapamycin (Rapa). We designed a reporter system based on fluorescence translocation by signal peptide reconstitution. Herein, signal peptides are activated by conditional protein splicing without the need for refolding into a functional tertiary structure, thus eliminating false positives and negatives due to mere binding or misfolding. The developed biosensor demonstrated excellent sensitivity with a limit of detection of 0.1 nM, and it was able to screen the agonist and antagonist of Rapa. The developed cell-based sensing system could contribute to improving the screening system aimed to identify the natural mimetics of Rapa and potential drug candidates.

Ultrabright Fluorescence Readout of an Inkjet-Printed Immunoassay Using Plasmonic Nanogap Cavities

Fluorescence-based microarrays are promising diagnostic tools due to their high throughput, small sample volume requirements, and multiplexing capabilities. However, their low fluorescence output has limited their implementation for in vitro diagnostics applications in point-of-care (POC) settings. Here, by integration of a sandwich immunoassay microarray within a plasmonic nanogap cavity, we demonstrate strongly enhanced fluorescence which is critical for readout by inexpensive POC detectors. The immunoassay consists of inkjet-printed antibodies on a polymer brush which is grown on a gold film. Colloidally synthesized silver nanocubes are placed on top and interact with the underlying gold film creating high local electromagnetic field enhancements. By varying the thickness of the brush from 5 to 20 nm, up to a 151-fold increase in fluorescence and 14-fold improvement in the limit-of-detection is observed for the cardiac biomarker B-type natriuretic peptide (BNP) compared to the unenhanced assay, paving the way for a new generation of POC clinical diagnostics.

The biotechnological potential of marine bacteria in the novel lineage of Pseudomonas pertucinogena

Marine habitats represent a prolific source for molecules of biotechnological interest. In particular, marine bacteria have attracted attention and were successfully exploited for industrial applications. Recently, a group of Pseudomonas species isolated from extreme habitats or living in association with algae or sponges were clustered in the newly established Pseudomonas pertucinogena lineage. Remarkably for the predominantly terrestrial genus Pseudomonas, more than half (9) of currently 16 species within this lineage were isolated from marine or saline habitats. Unlike other Pseudomonas species, they seem to have in common a highly specialized metabolism. Furthermore, the marine members apparently possess the capacity to produce biomolecules of biotechnological interest (e.g. dehalogenases, polyester hydrolases, transaminases). Here, we summarize the knowledge regarding the enzymatic endowment of the marine Pseudomonas pertucinogena bacteria and report on a genomic analysis focusing on the presence of genes encoding esterases, dehalogenases, transaminases and secondary metabolites including carbon storage compounds.

Fluorescence-based bioassays for the detection and evaluation of food materials

We summarize here the recent progress in fluorescence-based bioassays for the detection and evaluation of food materials by focusing on fluorescent dyes used in bioassays and applications of these assays for food safety, quality and efficacy. Fluorescent dyes have been used in various bioassays, such as biosensing, cell assay, energy transfer-based assay, probing, protein/immunological assay and microarray/biochip assay. Among the arrays used in microarray/biochip assay, fluorescence-based microarrays/biochips, such as antibody/protein microarrays, bead/suspension arrays, capillary/sensor arrays, DNA microarrays/polymerase chain reaction (PCR)-based arrays, glycan/lectin arrays, immunoassay/enzyme-linked immunosorbent assay (ELISA)-based arrays, microfluidic chips and tissue arrays, have been developed and used for the assessment of allergy/poisoning/toxicity, contamination and efficacy/mechanism, and quality control/safety. DNA microarray assays have been used widely for food safety and quality as well as searches for active components. DNA microarray-based gene expression profiling may be useful for such purposes due to its advantages in the evaluation of pathway-based intracellular signaling in response to food materials.

Initial photophysical characterization of the proteorhodopsin optical proton sensor (PROPS)

Fluorescence is not frequently used as a tool for investigating the photocycles of rhodopsins, largely because of the low quantum yield of the retinal chromophore. However, a new class of genetically encoded voltage sensors is based upon rhodopsins and their fluorescence. The first such sensor reported in the literature was the proteorhodopsin optical proton sensor (PROPS), which is capable of indicating membrane voltage changes in bacteria by means of changes in fluorescence. However, the properties of this fluorescence, such as its lifetime decay components and its origin in the protein photocycle, remain unknown. This paper reports steady-state and nanosecond time-resolved emission of this protein expressed in two strains of Escherichia coli, before and after membrane depolarization. The voltage-dependence of a particularly long lifetime component is established. Additional work to improve quantum yields and improve the general utility of PROPS is suggested.

A signal-on fluorosensor based on quench-release principle for sensitive detection of antibiotic rapamycin

An antibiotic rapamycin is one of the most commonly used immunosuppressive drugs, and also implicated for its anti-cancer activity. Hence, the determination of its blood level after organ transplantation or tumor treatment is of great concern in medicine. Although there are several rapamycin detection methods, many of them have limited sensitivity, and/or need complicated procedures and long assay time. As a novel fluorescent biosensor for rapamycin, here we propose "Q'-body", which works on the fluorescence quench-release principle inspired by the antibody-based quenchbody (Q-body) technology. We constructed rapamycin Q'-bodies by linking the two interacting domains FKBP12 and FRB, whose association is triggered by rapamycin. The fusion proteins were each incorporated position-specifically with one of fluorescence dyes ATTO520, tetramethylrhodamine, or ATTO590 using a cell-free translation system. As a result, rapid rapamycin dose-dependent fluorescence increase derived of Q'-bodies was observed, especially for those with ATTO520 with a lowest detection limit of 0.65 nM, which indicates its utility as a novel fluorescent biosensor for rapamycin.

Application of fluorescent proteins in tumor research

Fluorescent proteins have been applied in multiple tumor research fields, including tumor cell growth, invasion, metastasis, angiogenesis, the interaction between tumor cells and host cells, and antitumor drugs. Fluorescent imaging has enabled what was formerly invisible to be seen clearly in vivo with fluorescent proteins. This article will make a brief review of the application of fluorescent proteins in tumor research.