Narrow Results

Glucose-, galactose- and lactose-containing photosensitizers based on derivatives of chlorophyll a and bacteriochlorophyll a were synthesized with the use of [3+2] cycloaddition between sugar azides and triple bond derivatives of chlorins and bacteriochlorins. Unlike bacteriochlorin cycloimide, chlorin was detected to form a Cu-complex during the click reaction. An approach to the synthesis of metal-free glycosylated chlorins was developed with the use of "protection" by Zn²⁺ cation and subsequent demetalation. It is based on the action of alkynyl chlorin e₆ derivative Zn-complex, which is resistant to the substitution by copper cation. Bacteriochlorin p cycloimide conjugate with per-acetylated β-D-lactose was obtained and shown to become water-soluble after unblocking of the lactose hydroxy functions. NMR studies allowed for the elucidation of structure, tautomeric form and conformation of the obtained compounds.

This review summarizes the applications of metallophthalocyanine (MPc) and metallo-porphyrin (MP) complexes as electrocatalysts immobilized onto various electrodes for the detection of hydrogen peroxide and glucose. The uses of MPc and MP complexes as electron mediators for the detection of glucose at glucose oxidase modified surfaces are discussed.

The synthesis of derivatives bearing glucose or galactose units linked by an acrylate spacer to one free meso position of a bis-aryl-porphyrin macrocycle was developed and characterized by standard spectroscopic techniques. The new mono-substituted gluco- and galacto-porphyrin derivatives 5–8 present an alternative to the widespread tetra-aryl porphyrin functionalization. Singlet oxygen studies showed a comparable singlet oxygen production with TPP. Furthermore, the less bulky architectures here synthesized present an opportunity to enhance the PDT and PDI capabilities of glycoporphyrins with a simple synthetic modification at one of the meso positions.

The development of peroxidase mimics with enhanced peroxidase-like activity is critical to building a convenient and fast glucose colorimetric sensor. Herein, a porphyrin-based conjugated microporous polymer (FePCMP) was synthesized through a Pd-/CuI catalyzed Sonogashira coupling reaction. The FePCMP exhibited specific and superior POD-like activity evaluated by the fast oxidation of 3,3$\prime$,5,5$\prime$-tetramethylbenzidine (a chromogenic substrate, TMB) to form the blue product (oxTMB) in the presence of H₂O₂. The outstanding POD-like activity is mainly ascribed to the Fe-N₄ active sites and the cross-linked porous framework of FePCMP. Furthermore, the FePCMP was applied in selective colorimetric detection of glucose through a glucose oxidase biocatalytic cascade reaction with a low detection limit (LOD) of 0.031 $\mu$M in the linear range of 0.2–5 $\mu$M. This study not only provided a new method for the design and synesis of specific POD-like nanozymes, but also the prepared FePCMP can be used as a POD-like enzyme for the colorimetric detection of other molecules, such as cholesterol, acetylcholine, etc.

We report on the sensitive detection of glucose using silicon nanowire array field-effect-transistor (SiNW-FET) upon illumination. The uniformly distributed and size-controlled SiNWs were fabricated by "top-down" approach. The fabricated SiNW-FET device was evaluated for detection of glucose in the range of 100–900 mg/dL. The SiNW-FET shows enhanced sensitivity of 0.988 ± 0.030 nA (mg/dl)^-1 upon illumination at 480 nm light as compared to without illumination as 0.486 ± 0.014 nA (mg/dL)^-1. The presented SiNW-FET device is fast, stable and sensitive to light as well as to bio analyte, and hence can be utilized as sensitive biological sensing platform.

In this study, a novel imprinted polymer based on 3-aminophenylboronic acid (APBA)-functionalized CdTe quantum dots (QDs) was synthesized and used to sensitively and selectively detect glucose. In the process of synthesis, the boronic acid in the APBA could combine covalently with vicinal diol compounds, directing imprinting process, and the APBA-modified CdTe QDs were used as the solid supports. By this method, the prepared molecular imprinting polymers (MIPs)-APBA/CdTe QDs show high selectivity, high sensitivity and good stability. Under optimal conditions, a linear relationship was obtained covering the linear range of 0–1.5mmol/L with a correlation coefficient of 0.99833 and a high imprinting factor about 5.71. Furthermore, the prepared MIPs-APBA/CdTe QDs were successfully applied to detect glucose in human serum samples. This work provides a new way to synthesize an excellent stability and efficient imprinted polymer based on CdTe QDs for convenient, fast and highly selective detection of glucose.

The direct synthesis of metal-organic frameworks (MOFs) with acidic and basic active sites is challenging due to the introduction of functional groups by post-functionalization method often jeopardize the framework integrity. Herein, we report the direct synthesis of acid-base bi-functional MOFs with tuning acid-base strength. Employing modulated hydrothermal (MHT) approach, microporous MOFs named UiO-66-NH₂ was prepared. Through the ring-opening reaction of 1,3-propanesultone with amino group, UiO-66-NH₂-SO₃H-type catalysts can be obtained. The synthesized catalysts were well characterized and their catalytic performances were evaluated in one-pot glucose to 5-HMF conversion. Results revealed the acid-base bi-functional catalyst possessed high activity and excellent stability. This work provides a general and economically viable approach for the large-scale synthesis of acid-base bi-functional MOFs for their potential use in catalysis field.

In this paper, a new and one-pot electrodeposition method was expanded for the preparation of NiS nanoparticles-based electrochemical biosensor using metal-ion complexes as a precursor. Thioacetamide was used to control the production rate of NiS nanoparticles for the first time. The proposed electrochemical sensor was characterized by energy dispersive X-ray spectroscopy (EDX), field emission scanning electron microscope (FESEM), cyclic voltammograms (CV), and electrochemical impedance spectra (EIS). Experiment parameters were optimized. Under the optimized condition, the prepared NiS-based biosensor exhibited excellent electrocatalytic oxidation of H₂O₂ and glucose due to their small size. It provided fast and sensitive strategy for detecting H₂O₂ and glucose in the range of 1–5000 and 1–1000$\mu$M. The detection limit of 0.257 and 0.3$\mu$M was obtained for H₂O₂ and glucose. The mechanisms were also analyzed. The proposed biosensor exhibited excellent anti-interference and repeatability. Furthermore, it was applied in the actual sample analysis, such as human blood serum.

The ability to control the shape, structure and faceting characteristics of bimetallic alloy nanocrystals (NCs) has been vital for designing a catalyst with excellent activity and durability in fuel cells. However, it has remained a significant challenge to synthesize platinum–copper (Pt–Cu) alloy NCs with controlled structure and exposed facets. Herein, Pt–Cu alloy NCs with different shapes, structures and facets were synthesized via a one-step direct chemical co-reduction method employing various glucose concentrations. The results showed that the prepared Pt–Cu alloy NCs exhibited very interesting facet-dependent electrocatalytic properties for ethylene glycol oxidation. In comparison with other prepared Pt–Cu alloy NCs and commercial Pt/C, Pt–Cu alloy NPs with (111)-dominant facets showed higher electrocatalytic activity and durability for ethylene glycol oxidation. Alloy NPs showing prominent electrocatalytic performance were attributed to the predominant (111) facets on NP surfaces serving as catalytic active sites, in addition to added Cu providing unique electronic and synergistic effects. The present work highlighted that these NPs with (111)-dominant facets were indeed promising candidates as electrocatalysts with excellent activity and superior durability.

A novel titanium dioxide–graphene–polyaniline (TiO₂–RGO–PANI) hybrid was prepared by the one-pot method and used as a nonenzymatic electrochemical sensor for glucose detection. The composition and structural morphology of the as-prepared composites were determined by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The characterization results showed that TiO₂–RGO–PANI is mainly composed of Ti, O, C and N and their weight percentages are 67.68%, 21.57%, 10.70% and 0.05%, respectively, indicating that the TiO₂–RGO–PANI composite catalyst has been successfully prepared and presents a poriferous coral structure. A series of electrochemical tests such as cyclic voltammetry tests declared that TiO₂–RGO–PANI composite possessed a low limit of detection (LOD) (7.46$\mu$M), good repeatability, selectivity and stability. In the concentration range of 10–180$\mu$M, the hybrid presented linear diffusion, and the linear equation was $I_{pa}=0.21338+0.01392$ (C/mM), the correlation coefficient $R^2=0.9912$. In addition, the comparison of the merits of this proposed electrode with some recent nonenzymatic glucose sensors indicates that this highly sensitive TiO₂–RGO–PANI complex glucose sensor provides a simple, low-cost, nonenzymatic method for glucose detection, and has promising applications in clinical diagnostics and medical analysis.

It is of great significance to prepare electrochemical glucose sensors with high selectivity and stability via effective and rapid methods. In this work, the self-support electrode with copper and nickel-based oxide is prepared by chemical-etching reaction which occurred under the property of electrochemical potential difference. In this processing, nickel foam is etched selectively by Cu${}^{2+}$ ions and they not only act as self-supporting electrode substrate, but also as nickel ions precursor of NiO. Moreover, the reaction can be completely satisfied on 30 min at room temperature. As a self-supporting electrode nonenzymic glucose electrochemical sensor, the electrode exhibited a wide linear range (0.04–3.00mM), low detection limit (0.02mM) with high sensitivity of 1096$\mu A\cdot {\mathrm{\text{mM}}}^{-1}\cdot {\mathrm{\text{cm}}}^{-2}$ and good selectivity, repeatability and stability. Furthermore, the application of the prepared sensor provides an avenue for the application of the transition metal materials in the field of electrochemical sensing.

The morphology of nanomaterials plays an important role in the electrochemical sensing performance. Herein, the morphology-dependent electrochemical sensing properties of NiCo₂O₄ for glucose were studied. NiCo₂O₄ with one-dimensional (1D) rod structure or two-dimensional (2D) sheet structure was synthesized by just changing solvent composition. The morphology, structure and electrochemical sensing performance of NiCo₂O₄ were characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and amperometric methods. The results of CV characterization show that the magnitude of the oxidation peak current increase obtained on rod-like NiCo₂O₄ is nearly two times higher than that of sheet-like NiCo₂O₄, which is due to the faster electron transfer rate of rod-like NiCo₂O₄. Rod-like NiCo₂O₄ exhibited higher electrocatalytic activity toward glucose oxidation with a wide linear range of 0.02–5.1mM, a low detection limit of 2.0$\mu$M and an ultrahigh sensitivity of 2040$\mu$A$\cdot$mM${}^{-1}$$\cdot$cm${}^{-2}$. Our findings offer a novel morphology-controllable synthesis strategy to understand the morphology impact on the electrochemical performances of NiCo₂O₄, and represent a facile design of electrocatalysts for sensors.

One of the major challenges in imaging biological tissues using optical techniques, such as optical coherence tomography (OCT), is the lack of light penetration due to highly turbid structures within the tissue. Optical clearing techniques enable the biological samples to be more optically homogeneous, allowing for deeper penetration of light into the tissue. This study investigates the effect of optical clearing utilizing various concentrations of glucose solution (10%, 30%, and 50%) on porcine skin. A gold-plated mirror was imaged beneath the tissue and percentage clearing was determined by monitoring the change in reflected light intensity from the mirror over time. The ratio of percentage clearing per tissue thickness for 10%, 30% and 50% glucose was determined to be 4.7 ±1.6% mm^-1 (n = 6), 10.6 ±2.0% mm^-1 (n = 7) and 21.8 ±2.2% mm^-1 (n = 5), respectively. It was concluded that while higher glucose concentration has the highest optical clearing effect, a suitable concentration should be chosen for the purpose of clearing, considering the osmotic stress on the tissue sample.

Noninvasive glucose monitoring development is critical for diabetic patient continuous monitoring. However, almost all the available devices are invasive and painful. Noninvasive methods such as using spectroscopy have shown some good results. Unfortunately, the drawback was that the tungsten halogen lamps usage that is impractical if applied on human skin. This paper compared the light emitting diode (LED) to traditional tungsten halogen lamps as light source for glucose detection where the type of light source plays an important role in achieving a good spectrum quality. Glucose concentration measurement has been developed as part of noninvasive technique using optical spectroscopy. Small change and overlapping in tungsten halogen results need to replace it with a more convenient light source such as LED. Based on the result obtained, the performance of LED for absorbance spectrum gives a significantly different and is directly proportional to the glucose concentration. The result shows a linear trend and successfully detects lowest at 60 to 160 mg/dL glucose concentration.

Multivariate calibration is an important tool for spectroscopic measurement of analyte concentrations. We present a detailed study of a hybrid multivariate calibration technique, constrained regularization (CR), and demonstrate its utility in noninvasive glucose sensing using Raman spectroscopy. Similar to partial least squares (PLS) and principal component regression (PCR), CR builds an implicit model and requires knowledge only of the concentrations of the analyte of interest. Calibration is treated as an inverse problem in which an optimal balance between model complexity and noise rejection is achieved. Prior information is included in the form of a spectroscopic constraint that can be obtained conveniently. When used with an appropriate constraint, CR provides a better calibration model compared to PLS in both numerical and experimental studies.

We propose a novel optical method for glucose measurement based on diffuse photon-pair density wave (DPPDW) in a multiple scattering medium (MSM) where the light scattering of photon-pair is induced by refractive index mismatch between scatters and phantom solution. Experimentally, the DPPDW propagates in MSM via a two-frequency laser (TFL) beam wherein highly correlated pairs of linear polarized photons are generated. The reduced scattering coefficient ${\mu }_{2s}^{\prime }$ and absorption coefficient ${\mu }_{2a}$ of DPPDW are measured simultaneously in terms of the amplitude and phase measurements of the detected heterodyne signal under arrangement at different distances between the source and detection fibers in MSM. The results show that the sensitivity of glucose detection via glucose-induced change of reduced scattering coefficient ($\delta {\mu }_{2s}^{\prime }$) is 0.049%mM${}^{-1}$ in a 1% intralipid solution. In addition, the linear range of $\delta {\mu }_{2s}^{\prime }$ vs glucose concentration implies that this DPPDW method can be used to monitor glucose concentration continuously and noninvasively subcutaneously.

Optical immersion clearing is a technique that has been widely studied for more than two decades and that is used to originate a temporary transparency effect in biological tissues. If applied in cooperation with clinical methods it provides optimization of diagnosis and treatment procedures. This technique turns biological tissues more transparent through two main mechanisms — tissue dehydration and refractive index (RI) matching between tissue components. Such matching is obtained by partial replacement of interstitial water by a biocompatible agent that presents higher RI and it can be completely reversible by natural rehydration in vivo or by assisted rehydration in ex vivo tissues. Experimental data to characterize and discriminate between the two mechanisms and to find new ones are necessary. Using a simple method, based on collimated transmittance and thickness measurements made from muscle samples under treatment, we have estimated the diffusion properties of glucose, ethylene glycol (EG) and water that were used to perform such characterization and discrimination. Comparing these properties with data from literature that characterize their diffusion in water we have observed that muscle cell membrane permeability limits agent and water diffusion in the muscle. The same experimental data has allowed to calculate the optical clearing (OC) efficiency and make an interpretation of the internal changes that occurred in muscle during the treatments. The same methodology can now be used to perform similar studies with other agents and in other tissues in order to solve engineering problems at design of inexpensive and robust technologies for a considerable improvement of optical tomographic techniques with better contrast and in-depth imaging.