Photochemical Coenzyme Regeneration in an Enzymatically Active Optical Material

A Novel Immunosensing Method Based on the Capture and Enzymatic Release of Sandwich-Type Covalently Conjugated Thionine-Gold Nanoparticles as a New Fluorescence Label Used for Ultrasensitive Detection of Hepatitis B Virus Surface Antigen

A novel ultrasensitive and simple amplified immunosensing strategy is designed based on a surface-enhanced fluorescence (SEF) nanohybrid made from covalently conjugated thionine-gold nanoparticles (GNP-Th), as a novel amplified fluorescence label, and magnetic nanoparticles (MNPs), as a biological carrier, used for hepatitis B virus surface antigen (HBsAg) detection. This immunosensing strategy operates on the basis of the capture and then release of the amplified fluorescence label. Capturing of the antiHBs-antibody (Ab)-modified GNP-thionine hybrid (GNP-Th-Ab) is carried out through the formation of a two-dimensional (sandwich) probe between this amplified label and antiHBs-antibody-modified magnetic nanoparticles (MNP-Ab), in the presence of a target antigen and using an external magnetic force. Afterward, releasing of the captured fluorescence label is performed using a protease enzyme (pepsin) by a digestion mechanism of grafted antibodies on the GNP-thionine hybrid. As a result of antibody digestion, the amplified fluorescent hybrids (labels) are released into the solution. To understand the mechanism of enhanced fluorescence, the nature of the interaction between thionine and gold nanoparticles is studied using the B3LYP density functional method. In such a methodology, several new mechanisms and structures are used simultaneously, including a SEF-based metal nanoparticle-organic dye hybrid, dual signal amplification in a two-dimensional probe between the GNP-thionine hybrid and MNPs, and a novel releasing method using protease enzymes. These factors improve the sensitivity and speed, along with the simplicity of the procedure. Under optimal conditions, the fluorescence signal increases with the increment of HBs antigen concentration in the linear dynamic range of 4.6 × 10-9 to 0.012 ng/mL with a detection limit (LOD) of 4.6 × 10-9 ng/mL. The proposed immunosensor has great potential in developing ultrasensitive and rapid diagnostic platforms.

Photobiocatalysis: Activating Redox Enzymes by Direct or Indirect Transfer of Photoinduced Electrons

Biocatalytic transformation has received increasing attention in the green synthesis of chemicals because of the diversity of enzymes, their high catalytic activities and specificities, and mild reaction conditions. The idea of solar energy utilization in chemical synthesis through the combination of photocatalysis and biocatalysis provides an opportunity to make the "green" process greener. Oxidoreductases catalyze redox transformation of substrates by exchanging electrons at the enzyme's active site, often with the aid of electron mediator(s) as a counterpart. Recent progress indicates that photoinduced electron transfer using organic (or inorganic) photosensitizers can activate a wide spectrum of redox enzymes to catalyze fuel-forming reactions (e.g., H₂ evolution, CO₂ reduction) and synthetically useful reductions (e.g., asymmetric reduction, oxygenation, hydroxylation, epoxidation, Baeyer-Villiger oxidation). This Review provides an overview of recent advances in light-driven activation of redox enzymes through direct or indirect transfer of photoinduced electrons.

Enzymatic AND logic gate with sigmoid response induced by photochemically controlled oxidation of the output

We report a study of a system which involves an enzymatic cascade realizing an AND logic gate, with an added photochemical processing of the output, allowing the gate's response to be made sigmoid in both inputs. New functional forms are developed for quantifying the kinetics of such systems, specifically designed to model their response in terms of signal and information processing. These theoretical expressions are tested for the studied system, which also allows us to consider aspects of biochemical information processing such as noise transmission properties and control of timing of the chemical and physical steps.

Brightly phosphorescent, environmentally responsive hydrogels containing a water-soluble three-coordinate gold(I) complex

Stimuli-responsive phosphorescent hydrogel microspheres have been synthesized by incorporating a water-soluble phosphorescent Au(I) complex, Na(8)[Au(TPPTS)(3)], TPPTS = tris(3,3',3''-trisulfonatophenyl)phosphine, into the polymer network of poly(N-isopropylacrylamide) (PNIPAM). Remarkable sensitization of the Au-centered emission takes place in the resulting phosphorescent hydrogels (by up to 2 orders of magnitude!) compared to that of the gold complex alone in pure water. Results of pH- and temperature-dependent luminescence titrations show that the sensitization is further magnified at physiological conditions, which is desirable for biomedical applications that will include bioimaging and drug delivery. The physical properties of PNIPAM microgels are not negatively impacted by the presence of the gold luminophore, as the colloidal crystallinity and phase transition properties remain intact. Phosphorescent microspheres have been further cross-linked by covalently bonding to neighboring particles, leading to brightly phosphorescent/high-water-content crystalline hydrogel networks with more stable crystallinity vs microgel soft crystals. These gel networks exhibit the same green phosphorescence seen in the hydrogel microspheres and pure Na(8)[Au(TPPTS)(3)] aqueous solutions with a broad unstructured profile and peak maximum at ∼525 nm. Dehydration leads to further emission sensitization and gradual blue shifts that can be fine-tuned to ultimately reach a turquoise emission at ∼490 nm in the freeze-dried form of the gel, corresponding to the emission of single crystals of Na(8)[Au(TPPTS)(3)], in agreement with the photoinduced Jahn-Teller distorted excited state model we reported earlier. Remarkable sensitivity to temperature and pH takes place in the emission enhancement with particularly favorable results at physiological conditions. The work herein represents a unique example of a stimulus-responsive phosphorescent hydrogel from a transition metal-based as opposed to lanthanide-based phosphor in an aqueous medium.

A thionine-based reversible redox sensor in a sequential injection system

According to the current demands of Green Analytical Chemistry and regarding the need for lower reagent consumption with improved analytical performance, an automatic methodology with a flow-through optosensor incorporating solid-phase spectrophotometric detection was developed. The sensor used in this work was based on the redox state of thionine whose oxidized form is blue and reduced form is colorless with monitoring carried out at 621 nm. This redox indicator was immobilized on gel beads and subsequently packed into a flow-through cell. It was then assembled into a sequential injection system and was shown to be an excellent alternative to monitor enzymatic redox reactions automatically as the redox catalysis is performed by glucose dehydrogenase. This enzyme is a representative dehydrogenase enzyme and uses NAD(+) as cofactor, promoting the oxidation of glucose to glucono-lactone and reduction of NAD(+) to NADH. The produced NADH promotes color depletion on the surface of the sensor. The calibration graph for glucose was linear between 5.74 x 10(-4) and 2.00 x 10(-3) mol L(-1) and detection limit was 1.72 x 10(-4) mol L(-1). Glucose concentration in different samples including sera, salines, perfusion solutions, powder for preparing oral solutions and solutions for hemodialysis was determined. The method proved to be reproducible with a RSD < 5% for glucose determinations.

Analytical chemistry with silica sol-gels: traditional routes to new materials for chemical analysis

The versatility of sol-gel chemistry enables us to generate a wide range of silica and organosilica materials with controlled structure, composition, morphology and porosity. These materials' hosting and recognition properties, as well as their wide-open structures containing many easily accessible active sites, make them particularly attractive for analytical purposes. In this review, we summarize the importance of silica sol-gels in analytical chemistry by providing examples from the separation sciences, optical and electrochemical sensors, molecular imprinting, and biosensors. Recent work suggests that manipulating the structure and composition of these materials at different scales (from molecular to macromolecular states and/or from micro- to meso- and/or macroporous levels) promises to generate chemical and biochemical sensing devices with improved selectivity and sensitivity.

Molecularly imprinted xerogels as platforms for sensing

Detection and quantification of analytes in clinical settings (e.g., routine blood testing), at home (e.g., glucose monitoring), in the field (e.g., environmental monitoring, war fighter protection, homeland security), and in the factory (e.g., worker health, beverage and food safety) is exceedingly challenging. Chemical sensors and biosensors have attracted considerable attention because of their perceived ability to meet these challenges. Chemical sensors exploit a recognition element in concert with a transduction strategy. When the recognition element is biological (e.g., antibody, aptamer, enzyme), the sensor is termed a biosensor. There is substantial literature on biosensing; however, there are compelling reasons for developing inexpensive, robust, and reusable alternatives for the expensive or unstable biorecognition elements. This Account summarizes recent research on designing and producing analyte-responsive materials based on molecularly imprinted xerogels.

Impact of coenzyme regeneration on the performance of an enzyme-based optical biosensor: a computational study

A mathematical model of a reagent-less optical sensing scheme composed of an enzymatic reaction coupled to light-controlled photochemical coenzyme regeneration is described. The model is based on previous experimental work describing the regeneration of NADPH from NADP(+) by excited state thionine coupled to the oxidation of isocitrate by isocitrate dehydrogenase. The system is capable of repeated isocitrate measurements without the addition of exogenous coenzyme. The model is simulated using numerical integration to determine the effect of regeneration on the sensor sensitivity, response time and maximum sample throughput rate. Prediction of these effects without a model is difficult due to activation and inhibition of the dehydrogenase by both forms of the coenzyme. The regeneration parameters, including thionine concentration and thionine excitation pattern, are varied to determine optimal sensor conditions to maximize performance. A periodic regeneration approach is found to be superior to a continuous regeneration approach as the former maximizes sensitivity and minimizes response time in most cases. In addition periodic regeneration results in a maximum sample throughput frequency that is achieved at a single optimal thionine level and is independent of the analyte concentration. In contrast the optimal thionine concentration during continuous regeneration varies with the sample analyte concentration. These findings highlight the importance of designing controllable regeneration for dehydrogenase-based optical biosensors.