Porous silicon-based optical microsensor for the detection of l-glutamine

A Molecularly Imprinted Polymer-Based Porous Silicon Optical Sensor for Quercetin Detection in Wines

Quercetin (QU), a bioactive flavonoid with significant nutritional and antioxidant properties, plays a vital role in the quality and stability of wine. This study presents the development of a molecularly imprinted polymer (MIP)-based optical sensor for the selective and sensitive detection of quercetin in red and white wines. The sensor combines the selective molecular recognition capabilities of MIPs with the optical properties of nanostructured porous silica (PSiO2) scaffolds, which serve as the transducer. MIP synthesis was achieved through a novel room-temperature vapor-phase polymerization method using pyrrole as the functional monomer. Computational simulations were used to optimize pyrrole interactions with QU and at the polymer level, to explore the binding interactions of QU with the resulting polypyrrole (PPy) matrix. Comprehensive characterization including UV-vis reflectance spectroscopy and advanced surface analyses confirmed successful MIP formation. The sensor exhibited high sensitivity in a dual linear response range (2.5-80 μM and 80-200 μM), with a detection limit of 0.7 μM. Selectivity tests against structurally similar flavonoids and antioxidants demonstrated a significantly higher response to quercetin, with an imprinting factor of 3.6. The sensor was validated using real wine samples, demonstrating the ability to detect quercetin without prior sample preparation. Results showed strong agreement with high-performance liquid chromatography (HPLC), confirming the sensor reliability. Additionally, the sensor exhibited excellent reusability with minimal signal variation (RSD = 2.6%) and good stability over 60 days (RSD = 3%). This work highlights the potential of MIP-based optical sensors for the real-time monitoring of bioactive compounds in complex food matrices, such as wine, offering a robust and cost-effective alternative for quality control applications.

A L-glutamine binding protein modified MNM structured optical fiber biosensor based on surface plasmon resonance sensing for detection of L-glutamine metabolism in vitro embryo culture

A surface plasmon resonance (SPR) optical fiber sensor with multimode-coreless-multimode (MNM) structure was developed, which modified by L-glutamine-binding protein (QBP) for detection of L-glutamine (Gln). The QBP was immobilized on the surface of gold films by chemical cross-linking and exhibited a binding affinity for L-glutamine. The conformation of QBP can be changed from the "open" to the "closed", which led to a red-shift of the SPR peak when QBP bounded to L-glutamine. There was a good linear correlation between is a dependence of the SPR peak on and the concentration of L-glutamine concentration in the range 10-100 μM, with a sensitivity of 10.797nm/log10[Gln] for L-glutamine in the in vitro embryo culture (IVC) medium environment, and the limit of detection (LOD) is 1.187 μM. This QBP-modified MNM structure optical fiber SPR sensor provides a new idea for the developmental potential assessment of embryos in the process of in vitro embryo culture.

Development of Optical Biosensor for the Detection of Glutamine in Human Biofluids Using Merocyanine Dye

Merocyanine dye based fluorescent organic compound has been synthesized for the detection of glutamine. The probe showed remarkable fluorescent intensity with glutamine through ICT (Intermolecular Charge Transfer Mechanism). Hence, it is tested for the detection of glutamine using colorimetric and fluorimetric techniques in physiological and neutral pH (7.2). Under optimized experimental conditions, the probe detects glutamine selectively among other interfering biomolecules. The probe has showed a LOD (lower limit of detection) of 9.6 × 10^-8 mol/L at the linear range 0-180 µM towards glutamine. The practical application of the probe is successfully tested in human biofluids.

Rapid and reagentless detection of thrombin in clinic samples via microfluidic aptasensors with multiple target-binding sites

A reusable and straightforward aptasensor with the implementation of open-ended porous silicon (OEPSi) membranes was introduced for thrombin detection. When passing through the nanochannels of OEPSi integrated in a microfluidic cell, thrombin in sample solution could be captured by thrombin-binding aptamers (TBA) immobilized along the inner walls. The formation of thrombin-aptamer complex causes refractive index changes which can be measured by reflective interferometric Fourier transform spectroscopy (RIFTS). And this flow-through configuration with OEPSi has proven more efficient in capturing thrombin than the flow-over configuration with closed-ended PSi. For higher sensitivity, we investigated how the pore size, ionic strength, pH and aptamers affected the thrombin-aptamer interaction in nanopores. Under optimized conditions, the limits of detection (LOD) for thrombin detection in the buffer and serum were ∼6.70 nM and ∼8.21 nM respectively and a wide linear detection range (10-1000 nM) was observed. More importantly, this work reveals the sensitivity of the label-free biosensor can be significantly improved by attaching newly designed aptamers with two thrombin-binding sites. This phenomenon also indicates the potential of aptamer probes in adjusting effective pore size and enhancing the interaction between aptamers and targets through meticulous sequence design. Furthermore, the proposed strategy has been applied in thrombin detection in clinic samples successfully, which was verified by Enzyme-Linked Immunosorbent Assays (ELISA).

On-demand Antimicrobial Treatment with Antibiotic-Loaded Porous Silicon Capped with a pH-Responsive Dual Plasma Polymer Barrier

Chronic wounds are a major socio-economic problem. Bacterial infections in such wounds are a major contributor to lack of wound healing. An early indicator of wound infection is an increase in pH of the wound fluid. Herein, we describe the development of a pH-responsive drug delivery device that can potentially be used for wound decontamination in situ and on-demand in response to an increase in the pH of the wound environment. The device is based on a porous silicon film that provides a reservoir for encapsulation of an antibiotic within the pores. Loaded porous silicon is capped with dual plasma polymer layers of poly(1,7-octadiene) and poly(acrylic acid), which provide a pH-responsive barrier for on-demand release of the antibiotic. We demonstrate that release of the antibiotic is inhibited in aqueous buffer at pH 5, whereas the drug is released in a sustainable manner at pH 8. Importantly, the released drug was bacteriostatic against the Pseudomonas aeruginosa wound pathogen. In the future, incorporation of the delivery device into wound dressings could potentially be utilized for non-invasive decontamination of wounds.

Femtomole Detection of Proteins Using a Label-Free Nanostructured Porous Silicon Interferometer for Perspective Ultrasensitive Biosensing

Nanostructured porous silicon (PS) is a promising material for label-free optical detection of biomolecules, though it currently suffers of limited clinical diagnostic applications due to insufficient sensitivity. In this regard, here we introduce an ultrasensitive and robust signal processing strategy for PS biosensors that relies on the calculation of the average value over wavelength of spectral interferograms, namely IAW, obtained on PS interferometer by subtraction (wavelength by wavelength) of reflection spectra acquired after adsorption of biomolecules inside the nanopores from a reference reflection spectrum recorded in acetate buffer. As a case study, we choose to monitor bovine serum albumin (BSA) unspecific adsorption, which has been often employed in the literature as a model for proof-of-concept studies of perspective biosensing applications. The proposed IAW signal processing strategy enables reliable detection of BSA at concentrations in the range from 150 pM to 15 μM (down to 3 orders of magnitude lower than those targeted in the current literature) using a PS interferometer operating in label-free mode without any amplification strategies, with good sample-to-sample reproducibility over the whole range of tested concentrations (%CV = 16% over 5 replicates) and good signal-to-noise ratio also at the lowest tested concentration (S/N ≈ 4.6 at 150 pM). A detection limit (DL) of 20 pM (20 femtomoles, 1 mL) is estimated from the sigmoidal function best fitting (R(2) = 0.989) IAW experimental data over the whole range of tested concentrations. This is the lowest DL that has been reported in the literature since the seminal paper of Sailor and co-workers (1997) on the use of PS interferometer for biosensing, and lowers of 4 orders of magnitude DL attained with label-free PS interferometers using conventional effective optical thickness (EOT) calculation through reflective interferometric Fourier transform spectroscopy. Accordingly, the IAW signal processing strategy envisage bringing PS optical transduction at the forefront of ultrasensitive label-free biosensing techniques, especially for point-of-care clinical analysis where low analyte concentrations have to be detected in a small amount of biological samples.

Production and optimization of L-glutaminase enzyme from Hypocrea jecorina pure culture

L-Glutaminase (L-glutamine amidohydrolase, EC 3.5.1.2) is the important enzyme that catalyzes the deamination of L-glutamine to L-glutamic acid and ammonium ions. Recently, L-glutaminase has received much attention with respect to its therapeutic and industrial applications. It acts as a potent antileukemic agent and shows flavor-enhancing capacity in the production of fermented foods. Glutaminase activity is widely distributed in plants, animal tissues, and microorganisms, including bacteria, yeasts, and fungi. This study presents microbial production of glutaminase enzyme from Hypocrea jecorina pure culture and determination of optimum conditions and calculation of kinetic parameters of the produced enzyme. The optimum values were determined by using sa Nesslerization reaction for our produced glutaminase enzyme. The optimum pH value was determined as 8.0 and optimum temperature as 50°C for the glutaminase enzyme. The Km and Vmax values, the kinetic parameters, of enzyme produced from Hypocrea jecorina, pure culture were determined as 0.491 mM for Km and 13.86 U/L for Vmax by plotted Lineweaver-Burk graphing, respectively. The glutaminase enzyme from H. jecorina microorganism has very high thermal and storage stability.

Micropatterned arrays of porous silicon: toward sensory biointerfaces

We describe the fabrication of arrays of porous silicon spots by means of photolithography where a positive photoresist serves as a mask during the anodization process. In particular, photoluminescent arrays and porous silicon spots suitable for further chemical modification and the attachment of human cells were created. The produced arrays of porous silicon were chemically modified by means of a thermal hydrosilylation reaction that facilitated immobilization of the fluorescent dye lissamine, and alternatively, the cell adhesion peptide arginine-glycine-aspartic acid-serine. The latter modification enabled the selective attachment of human lens epithelial cells on the peptide functionalized regions of the patterns. This type of surface patterning, using etched porous silicon arrays functionalized with biological recognition elements, presents a new format of interfacing porous silicon with mammalian cells. Porous silicon arrays with photoluminescent properties produced by this patterning strategy also have potential applications as platforms for in situ monitoring of cell behavior.

Stimulus-responsiveness and drug release from porous silicon films ATRP-grafted with poly(N-isopropylacrylamide)

In this report, we employ surface-initiated atom transfer radical polymerization (SI-ATRP) to graft a thermoresponsive polymer, poly(N-isopropylacrylamide) (PNIPAM), of controlled thickness from porous silicon (pSi) films to produce a stimulus-responsive inorganic-organic composite material. The optical properties of this material are studied using interferometric reflectance spectroscopy (IRS) above and below the lower critical solution temperature (LCST) of the PNIPAM graft polymer with regard to variation of pore sizes and thickness of the pSi layer (using discrete samples and pSi gradients) and also the thickness of the PNIPAM coatings. Our investigations of the composite's thermal switching properties show that pore size, pSi layer thickness, and PNIPAM coating thickness critically influence the material's thermoresponsiveness. This composite material has considerable potential for a range of applications including temperature sensors and feedback controlled drug release. Indeed, we demonstrate that modulation of the temperature around the LCST significantly alters the rate of release of the fluorescent anticancer drug camptothecin from the pSi-PNIPAM composite films.

Xe interacting with porous silicon

Thin films of porous silicon (PS), structurally characterized by HR-SEM, were studied using xenon Temperature Programmed Desorption (TPD) as a probe of its inner pores. Geometric hindrance of the depth desorbing population and multiple wall collisions result in a unique double-peak structure of the TPD curve. Surface-diffusion assisted adsorption mechanism into inner pores at 48 K is proposed as the origin of these unique TPD spectra. It is experimentally verified by mild Ne(+) sputtering prior to TPD which preferentially removes Xe population from the top surfaces. A pore-diameter limited desorption kinetic model that takes into account diffusion and pore depth well explains the governing parameters that determine the experimental observations. These results suggest that TPD may be employed as a highly sensitive, non-destructive surface area determination tool.

Microfabricated implants for applications in therapeutic delivery, tissue engineering, and biosensing

By adapting microfabrication techniques originally developed in the microelectronics industry novel devices for drug delivery, tissue engineering and biosensing have been engineered for in vivo use. Implant microfabrication uses a broad range of techniques including photolithography, and micromachining to create devices with features ranging from 0.1 to hundreds of microns with high aspect ratios and precise features. Microfabrication offers device feature scale that is relevant to the tissues and cells to which they are applied, as well as offering ease of en masse fabrication, small device size, and facile incorporation of integrated circuit technology. Utilizing these methods, drug delivery applications have been developed for in vivo use through many delivery routes including intravenous, oral, and transdermal. Additionally, novel microfabricated tissue engineering approaches propose therapies for the cardiovascular, orthopedic, and ocular systems, among others. Biosensing devices have been designed to detect a variety of analytes and conditions in vivo through both enzymatic-electrochemical reactions and sensor displacement through mechanical loading. Overall, the impact of microfabricated devices has had an impact over a broad range of therapies and tissues. This review addresses many of these devices and highlights their fabrication as well as discusses materials relevant to microfabrication techniques.

Specific detection of proteins using photonic crystal waveguides

Specific detection of proteins is demonstrated using planar photonic crystal waveguides. Using immobilized biotin as probe, streptavidin was captured, causing the waveguide mode cut-off to red-shift. The device was shown to detect a 2.5 nm streptavidin film with a 0.86 nm cut-off red-shift. An improved photonic crystal waveguide sensor design is also described and shown to have a 40% improved bulk refractive index response.

In vitro immunogenicity of silicon-based micro- and nanostructured surfaces

The increasing use of micro- and nanostructured silicon-based devices for in vivo therapeutic or sensing applications highlights the importance of understanding the immunogenicity of these surfaces. Four silicon surfaces (nanoporous, microstructured, nanochanneled, and flat) were studied for their ability to provoke an immune response in human blood derived monocytes. The monocytes were incubated with the surfaces for 48 h and the immunogenicity was evaluated based on the viability, shape factors, and cytokine expression. Free radical oxygen formation was measured at 18 h to elicit a possible mechanism invoking immunogenicity. Although no cytokines were significantly different comparing the response of monocytes on the tissue culture polystyrene surfaces to those on the micropeaked surfaces, on average all cytokines were elevated on the micropeaked surface. The monocytes on the nanoporous surface also displayed an elevated cytokine response, overall, but not to the degree of those on the micropeaked surface. The nanochanneled surface response was similar to that of flat silicon. Overall, the immunogenicity and biocompatibility of flat, nanochanneled, and nanoporous silicon toward human monocytes are approximately equivalent to tissue culture polystyrene.