A New Glucose-Selective Fluorescent Bisboronic Acid. First Report of Strong α-Furanose Complexation in Aqueous Solution at Physiological pH1

Reaction-Free Energies for Complexation of Carbohydrates by Tweezer Diboronic Acids

The accurate calculation of reaction-free energies (ΔrG°) for diboronic acids and carbohydrates is challenging due to reactant flexibility and strong solute-solvent interactions. In this study, these challenges are addressed with a semiautomatic workflow based on quantum chemistry methods to calculate conformational free energies, generate microsolvated solute structural ensembles, and compute ΔrG°. Workflow parameters were optimized for accuracy and precision while controlling computational costs. We assessed the accuracy by studying three reactions of diboronic acids with glucose and galactose, finding that the conformational entropy contributes significantly (by 3-5 kcal/mol at room temperature). Explicit solvent molecules improve the computed ΔrG° accuracy by about 4 kcal/mol compared to experimental data, though using 13 or more water molecules reduced precision and increased computational overhead. After fine-tuning, the workflow demonstrated remarkable accuracy, with an absolute error of about 2 kcal/mol compared to experimental ΔrG° and an average interquartile range of 2.4 kcal/mol. These results highlight the workflow's potential for designing and screening tweezer-like ligands with tailored selectivity for various carbohydrates.

Boronate Ester Hydrogels for Biomedical Applications: Challenges and Opportunities

Boronate ester (BE) hydrogels are increasingly used for biomedical applications. The dynamic nature of these molecular networks enables bond rearrangement, which is associated with viscoelasticity, injectability, printability, and self-healing, among other properties. BEs are also sensitive to pH, redox reactions, and the presence of sugars, which is useful for the design of stimuli-responsive materials. Together, BE hydrogels are interesting scaffolds for use in drug delivery, 3D cell culture, and biofabrication. However, designing stable BE hydrogels at physiological pH (≈7.4) remains a challenge, which is hindering their development and biomedical application. In this context, advanced chemical insights into BE chemistry are being used to design new molecular solutions for material fabrication. This review article summarizes the state of the art in BE hydrogel design for biomedical applications with a focus on the materials chemistry of this class of materials. First, we discuss updated knowledge in BE chemistry including details on the molecular mechanisms associated with BE formation and breakage. Then, we discuss BE hydrogel formation at physiological pH, with an overview of the main systems reported to date along with new perspectives. A last section covers several prominent biomedical applications of BE hydrogels, including drug delivery, 3D cell culture, and bioprinting, with critical insights on the design relevance, limitations and potential.

Ag@AuNP-Functionalized Capillary-Based SERS Sensing Platform for Interference-Free Detection of Glucose in Urine Using SERS Tags with Built-In Nitrile Signal

A Ag@AuNP-functionalized capillary-based surface-enhanced Raman scattering (SERS) sensing platform for the interference-free detection of glucose using SERS tags with a built-in nitrile signal has been proposed in this work. Capillary-based SERS capture substrates were prepared by connecting 4-mercaptophenylboronic acid (MBA) to the surface of the Ag@AuNP layer anchored on the inner wall of the capillaries. The SERS tags with a built-in interference-free signal could then be fixed onto the Ag@AuNP layer of the capillary-based capture substrate based on the distinguished feature of glucose, which can form a bidentate glucose-boronic complex. Thus, many "hot spots" were formed, which produced an improved SERS signal. The quantitative analysis of glucose levels was realized using the interference-free SERS intensity of nitrile at 2222 cm-1, with a detection limit of about 0.059 mM. Additionally, the capillary-based disposable SERS sensing platform was successfully employed to detect glucose in artificial urine, and the new strategy has great potential to be further applied in the diagnosis and control of diabetes.

Recent Progress in Diboronic-Acid-Based Glucose Sensors

Non-enzymatic sensors with the capability of long-term stability and low cost are promising in glucose monitoring applications. Boronic acid (BA) derivatives offer a reversible and covalent binding mechanism for glucose recognition, which enables continuous glucose monitoring and responsive insulin release. To improve selectivity to glucose, a diboronic acid (DBA) structure design has been explored and has become a hot research topic for real-time glucose sensing in recent decades. This paper reviews the glucose recognition mechanism of boronic acids and discusses different glucose sensing strategies based on DBA-derivatives-based sensors reported in the past 10 years. The tunable pK_a, electron-withdrawing properties, and modifiable group of phenylboronic acids were explored to develop various sensing strategies, including optical, electrochemical, and other methods. However, compared to the numerous monoboronic acid molecules and methods developed for glucose monitoring, the diversity of DBA molecules and applied sensing strategies remains limited. The challenges and opportunities are also highlighted for the future of glucose sensing strategies, which need to consider practicability, advanced medical equipment fitment, patient compliance, as well as better selectivity and tolerance to interferences.

Diboronate crosslinking: Introducing glucose specificity in glucose-responsive dynamic-covalent networks

Dynamic-covalent motifs are increasingly used for hydrogel crosslinking, leveraging equilibrium-governed reversible bonds to prepare viscoelastic materials with dynamic properties and self-healing character. The bonding between aryl boronates and diols is one dynamic-covalent chemistry of interest. The extent of network crosslinking using this motif may be subject to competition from ambient diols such as glucose; this approach has long been explored for glucose-directed release of insulin to control diabetes. However, the majority of such work has used phenylboronic acids (PBAs) that suffer from low-affinity glucose binding, limiting material responsiveness. Moreover, many PBA chemistries also bind with higher affinity to certain non-glucose analytes like fructose and lactate than they do to glucose, limiting their specificity of sensing and therapeutic deployment. Here, dynamic-covalent hydrogels are prepared that, for the first time, use a new diboronate motif with enhanced glucose binding-and importantly improved glucose specificity-leveraging the ability of rigid diboronates to simultaneously bind two sites on a single glucose molecule. Compared to long-used PBA-based approaches, diboronate hydrogels offer more glucose-responsive insulin release that is minimally impacted by non-glucose analytes. Improved responsiveness translates to more rapid blood glucose correction in a rodent diabetes model. Accordingly, this new dynamic-covalent crosslinking chemistry is useful in realizing more sensitive and specific glucose-responsive materials.

Boronic derivatization-based strategy for monoacylglycerol identification, isomer annotation and quantification

Monoacylglycerols (MAGs) are important signaling molecules involved in various diseases. However, it is challenge for direct detection of MAGs and isomers. Additionally, difficulties in isomer annotation hinders the comprehensive profiling of MAGs and hampers revealing isomers' contributions to diseases. Herein, a boronic derivatization-based strategy was developed for unambiguous identification, isomer annotation and quantification of MAGs in biological samples. 3-Nitrophenylboronic acid was selected as the derivatization reagent owing to its rapid and selective reactivity toward cis-diol moiety. First, a prediction model was established for MAG identification by the integration of m/z, isotopic distribution of boron, and retention time attributed by the carbon chain length and number of double bonds, which solved the difficulty of obtaining MAG standards. In addition, the designed derivatization reaction enabled the capture of thermally unstable sn-2 MAG isomers to ensure the chromatographic separation and direct MS detection. What's more, distinguished fragmentation patterns were discovered for derivatized MAG isomers, which allowed a novel and unambiguous isomer annotation. Furthermore, by considering the availability of standards, the quantification of MAGs was based on the development of calibration curves or relative quantification by internal standard. On this basis, the developed strategy was utilized for MAG identification and quantification in breast cancer samples, which suggested that MAGs could be regarded as potential biomarkers in breast cancer diagnosis or as indicators to trace the process of chemotherapy. It also helped make the puzzle complete by revealing that only one single isomer associated with the onset of disease was possible, instead of regarding them as a whole. Therefore, the boronic derivatization-based strategy facilitated the unambiguous identification, annotation and quantification of MAGs and isomers in biofluids, and would be beneficial for the mechanism studies of related diseases.

Connecting the Dynamics and Reactivity of Arylboronic Acids to Emergent and Stimuli-Responsive Material Properties

Over the past two decades, arylboronic acid-functionalized biomaterials have been used in a variety of sensing and stimuli-responsive scaffolds. Their diverse applications result from the diverse reactivity of arylboronic acids,...

Surface Engineered PLGA Nanoparticle for Threshold Responsive Glucose Monitoring and "Self-Programmed" Insulin Delivery

We have developed a reversible, biocompatible, "self-programmed" PLGA [poly(lactic-co-glycolic acid)] nanoparticle-based optical biosensor capable of sensing and continuous monitoring of glucose above the physiologically relevant threshold value (100-125 mg/dL) as well as "on-demand" insulin delivery via an "On-Off" technique. We have carefully surface engineered the PLGA nanoparticle using amino dextran-fluorescein (A-DexFl) and amino-phenyl boronic acid (A-PBA) to exploit the binding affinity of boronic acids with that of cis-1,2 diols of dextran/glucose. Initially, the dextran chains wrap the nanoparticle surface due to its high affinity toward A-PBA (K_b = 6.1 × 10⁶ M^-1). The close proximity of the fluorophores with that of A-PBA quenches the fluorescence, resulting in an "Off" state. On the addition of glucose, it competes with A-DexFl to bind with A-PBA. Above a certain threshold concentration of glucose, the binding affinity overcomes (K_b = 6.3 × 10⁷ M^-1) the dextran-A-PBA binding. This opens-up the wrapped A-DexFl chains from the nanoparticle surface and results in an increased distance between the fluorophore and A-PBA, triggering the "On" state. The activation of the On-Off state can be finely tuned in the desired range of physiologically relevant glucose concentrations by varying the ligand ratios on the PLGA surface. The nanoparticle core has also been used as an insulin reservoir to trigger the drug release in the "On" state. We have obtained ∼53% encapsulation efficiency and ∼20% loading efficiency for insulin loading. Once the glucose concentration falls beyond the detection range, the dextran chains collapse on the nanoparticle surface with a suspension in drug release. The process is solely controlled by the competition and multivalent binding affinity between glucose, A-DexFl, and A-PBA, which allows it to be "self-programmed" and "self-regulated" with continuous monitoring up to 8-10 cycles over a 72 h time period. A sustained drug release has been found with ∼70% of released drug over a period of 72 h, although this release is insignificant in the absence of glucose. Several control experiments have been performed to optimize the sensor design.

Tandem Quantification of Multiple Carbohydrates in Saliva Using Surface-Enhanced Raman Spectroscopy

The detection of carbohydrates in human body fluids is critical for disease diagnosis and healthy monitoring. Despite recent advances in glucose sensing, multiplex detection of different carbohydrates within a single assay that is capable of efficiently providing richer health information remains challenging. Herein, we report a versatile surface-enhanced Raman spectroscopy-based platform for the quantitative detection of monosaccharides (glucose, fructose, and galactose) in one test using a displace-and-trap mechanism. Moreover, due to the use of multiple optical interference-free (1800-2200 cm^-1) signal-independent Raman probes, the detection range of this platform (0.125-7 mg/dL) perfectly covers physiological concentrations, enabling the quantitative detection of glucose and galactose in clinical human saliva samples. This work provides a noninvasive and high-efficiency potential tool for the screening of clinical diabetes and other carbohydrate-related diseases.

Creation of glycoprotein imprinted self-assembled monolayers with dynamic boronate recognition sites and imprinted cavities for selective glycoprotein recognition

Glycoproteins are involved in the pathogenesis and development of many diseases and are used as biomarkers for disease diagnosis. It is highly desirable to develop highly sensitive and selective methods for the detection of glycoproteins without the use of antibodies. Imprinting of proteins represents one of the most challenging tasks. Glycoprotein imprinted self-assembled monolayers (SAMs) were created, for the first time, from an oligo(ethylene glycol) (OEG) terminated 1,2-dithiolane derivative linked through an alkyl chain incorporated with two amide groups (DHAP) and combined functional thiols of p-mercaptophenylboronic acid (PMBA) and p-aminothiophenol (PATP) in aqueous media, without the use of polymerization initiators. Combined action of PMBA and PATP was essential for the development of boronate recognition sites for glycoproteins at the physiological pH, attributed to the water molecule-mediated Lewis acid-base interactions between the electron-deficient PMBA and the electron-rich PATP. DHAP played key roles not only in cementation of imprinted cavities by means of double hydrogen bond networks through the amide groups but also in resistance to nonspecific protein binding by terminal OEG moieties, as well as hydrogen bond binding sites from the amide groups exposed to imprinted cavities. The created glycoprotein imprinted SAMs showed excellent recognition selectivity of target glycoproteins. The strategy for tailor-made glycoprotein imprinted SAMs explores a new avenue to the creation of intelligent biomaterials and fabrication of chemosensors.

Boronic acid sensors with double recognition sites: a review

Boronic acids reversibly and covalently bind to Lewis bases and polyols, which facilitated the development of a large number of chemical sensors to recognize carbohydrates, catecholamines, ions, hydrogen peroxide, and so on. However, as the binding mechanism of boronic acids and analytes is not very clear, it is still a challenge to discover sensors with high affinity and selectivity. In this review, boronic acid sensors with two recognition sites, including diboronic acid sensors, and monoboronic acid sensors having another group or binding moiety, are summarized. Owing to double recognition sites working synergistically, the binding affinity and selectivity of sensors can be improved significantly. This review may help researchers to sort out the binding rules and develop ideal boronic acid-based sensors.

Boron-Conjugated Pyrenes as Fluorescence-Based Molecular Probes and Security Markers

Boron-embedded aromatic hydrocarbons are a class of molecules known for their distinct electronic and/or optoelectronic properties and are thus suitable for many potential applications. Among those, boronic ester and acid containing molecules have been widely used for sensing and molecular recognition applications, respectively. We compared the sensing and molecular recognition properties of two boron-containing pyrene derivatives for fluoride and glucose sensing applications. The presence of four boronate ester groups enabled fluoride ion sensing at the μM level. The boronic acid derivative is very selective towards glucose compared to other saccharides. Furthermore, we used the mechano-responsive fluorescence changes and self-assembly of these derivatives, respectively, for fluorescence-based inkless and ink (water)-based writing in invisible security labeling applications.

Molecular Design of a New Diboronic Acid for the Electrohydrodynamic Monitoring of Glucose

A new dicationic diboronic acid structure, DBA2+, was designed to exhibit good affinity (K_d ≈1 mm) and selectivity toward glucose. Binding of DBA2+ to glucose changes the pK_a of DBA2+ from 9.4 to 6.3, enabling opportunities for detection of glucose at physiological pH. Proton release from DBA2+ is firmly related to glucose concentrations within the physiologically relevant range (0-30 mm), as verified by conductimetric monitoring. Negligible interference from other sugars (for example, maltose, fructose, sucrose, lactose, and galactose) was observed. These results demonstrate the potential of DBA2+ for selective, quantitative glucose sensing. The nonenzymatic strategy based on electrohydrodynamic effects may enable the development of stable, accurate, and continuous glucose monitoring platforms.

Boronic Acid Appended Naphthyl-Pyridinium Receptors as Chemosensors for Sugars

There remains a need in clinics and research to have simple and sensitive detection systems that allow the detection and quantification of sugar markers of biomedical relevance such as sugars lactulose and mannitol for noninvasive gut permeability assessment. We have prepared a new class of boronic acid-appended naphthyl-pyridinium receptor compounds as chemosensors. These were studied for their ability to act as modular internal charge transfer (ICT) fluorescent probes or donor/acceptor pair ensembles where the receptor compound can act as a quencher for an anionic dye. As an ICT sensor, fluorescence intensity increased upon diol recognition, which stems from the neutralization of the pyridinium nitrogen that is perturbing the chromophoric properties. We found these ICT probes provide good sensitivity for disaccharide lactulose with low micromolar detection and quantification limits. In addition, their ability to form a non-fluorescent ground state complex with anionic reporter dyes, such as HPTS or TSPP, was examined as probes for various sugars. We have identified three receptor/quencher compounds with high quenching efficiency for anionic dyes. Subsequently, a range of sugars and sugar derivatives were tested for chemosenstivity of our probes. This study illustrates an approach for designing boronic acid-based chemoreceptors for the recognition and quantification of sugars and sugar derivatives.

Boronic Derivatization of Monoacylglycerol and Monitoring in Biofluids

Monoacylglycerols (MAGs) are active mediators involved in multiple biological processes closely related to the pathological development of diabetes, obesity, and cancers. Sensitive and unambiguous detection of MAGs is thus essential; however, previous methods are both indirect and labor-intensive. Herein, we developed a straightforward approach by derivatization of MAGs with 3-nitrophenylboronic acid (3-NPB) for sensitive and selective analysis in cell lysates, tissues, and serums by mass spectrometry (MS). Reaction occurring between boronic acid and cis-diol moiety of MAGs blocked the formation of multiple adduct ions and tuned MAGs to negatively charged carrying species. In addition, the characteristic isotopic distribution of boron specialized the presence of modified MAGs in MS and led to distinctive identification. To eliminate endogenous interferences, we further introduced isotopic labeled d₄-NPB equivalently premixed with d₀-NPB to perform MAG derivatization, which resulted in rapid identification of modified MAGs in biofluids by displaying doublet peak characteristics. A comparative quantification approach was thereafter evoluted to reveal the amount variation of MAGs by d₀-NPB and d₄-NPB separately derivatized in different pathological tissue and serum samples. The presently developed NPB-based derivatization approach is expected to be essential in the metabolic study of MAG-related diseases.

Fabrication and Characterization of a Highly-Sensitive Surface-Enhanced Raman Scattering Nanosensor for Detecting Glucose in Urine

Herein we utilized coordination interactions to prepare a novel core-shell plasmonic nanosensor for the detection of glucose. Specifically, Au nanoparticles (NPs) were strongly linked with Ag+ ions to form a sacrificial Ag shell by using 4-aminothiophenol (4-PATP) as a mediator, which served as an internal standard to decrease the influence of the surrounding on the detection. The resultant Au-PATP-Ag core-shell systems were characterized by UV-vis spectroscopy, transmission electron microscopy, and surface-enhanced Raman scattering (SERS) techniques. Experiments performed with R6G (rhodamine 6G) and CV (crystal violet) as Raman reporters demonstrated that the Au@Ag nanostructure amplified SERS signals obviously. Subsequently, the Au@Ag NPs were decorated with 4-mercaptophenylboronic acid (4-MPBA) to specifically recognize glucose by esterification, and a detection limit as low as 10⁻⁴ M was achieved. Notably, an enhanced linearity for the quantitative detection of glucose (R² = 0.995) was obtained after the normalization of the spectral peaks using 4-PATP as the internal standard. Finally, the practical applicability of the developed sensing platform was demonstrated by the detection of glucose in urine with acceptable specificity.

Controlled synthesis of soluble conjugated polymeric nanoparticles for fluorescence detection

Highly fluorescent soluble conjugated polymeric nanoparticles (SCPNs) were synthesized in confined nanoreactors and used for fluorescence sensing of glucose and Fe ion.

Recent advances in boronic acid-based optical chemosensors

This minireview highlights the developments in optical chemosensors from 2014 to 2016 that utilise the boronic acid interaction with polyols or Lewis bases.

High performance boronic acid-containing hydrogel for biocompatible continuous glucose monitoring

Rapid and robust hydrogels are essential in realizing continuous glucose monitoring in diabetes monitoring.

Selective Recognition of d-Aldohexoses in Water by Boronic Acid-Functionalized, Molecularly Imprinted Cross-Linked Micelles

Molecular imprinting within cross-linked micelles using 4-vinylphenylboronate derivatives of carbohydrates provided water-soluble nanoparticle receptors selective for the carbohydrate templates. Complete differentiation of d-aldohexoses could be achieved by these receptors if a single inversion of hydroxyl occurred at C2 or C4 of the sugar or if two or more inversions took place. Glycosides with a hydrophobic aglycan displayed stronger binding due to increased hydrophobic interactions.

Self-assembly of a “double dynamic covalent” amphiphile featuring a glucose-responsive imine bond

Glucose recognition via in situ formation of supramolecular vesicular aggregates that involve two dynamic covalent bonds.

Lighting up sugars: fluorescent BODIPY–gluco-furanose and –septanose conjugates linked by direct B–O–C bonds

O-BODIPY–glucose conjugates are linked through covalent B–O–C(glucose) bonds, and feature a rare instance of the unnatural septanose form of glucose.

Bioinspired synthesis of poly(phenylboronic acid) microgels with high glucose selectivity at physiological pH

A microgel that is more sensitive towards glucose than to other saccharides is made of 4-vinylphenylboronic acid crosslinked withN,N′-bis(propene)perylene-3,4,9,10-tetracarboxyldiimide.

Boronic acid-modified poly(amidoamine) dendrimers as sugar-sensing materials in water

High-affinity carbohydrate receptors were developed by appending boronic acids to the surface of PAMAM dendrimers. These multivalent hosts were used to discriminate simple sugars in neat water using pattern recognition and optical spectroscopy techniques.

Construction of highly sensitive surface-enhanced Raman scattering (SERS) nanosensor aimed for the testing of glucose in urine

A facile, highly sensitive “turn on” SERS nanosensor for the detection of glucose in urine has been developed based on the aggregation of the 4-mercaptophenylboronic acid decorated silver nanoparticles in the specific bonding to glucose.

A new boronic acid fluorescent sensor based on fluorene for monosaccharides at physiological pH

Fluorescent boronic acids are very useful fluorescent sensor for detection of biologically important saccharides. Herein we synthesized a new fluorene-based fluorescent boronic acid that shows significant fluorescence changes upon addition of saccharides at physiological pH. Upon addition of fructose, sorbitol, glucose, galactose, ribose, and maltose at different concentration to the solution of 7-(dimethylamino)-9,9-dimethyl-9H-fluoren-2-yl-2-boronic acid (7-DMAFBA, 1), significant decreases in fluorescent intensity were observed. It was found that this boronic acid has high affinity (K(a)=3582.88 M(-1)) and selectivity for fructose over glucose at pH=7.4. The sensor 1 showed a linear response toward d-fructose in the concentrations ranging from 2.5×10(-5) to 4×10(-4) mol L(-1) with the detection limit of 1.3×10(-5) mol L(-1).

Sugar-Responsive Pseudopolyrotaxane Composed of Phenylboronic Acid-Modified Polyethylene Glycol and γ-Cyclodextrin

We have designed a sugar-responsive pseudopolyrotaxane (PPRX) by combining phenylboronic acid-modified polyethylene glycol (PBA–PEG) and γ-cyclodextrin. Phenylboronic acid (PBA) was used as a sugar-recognition motif in the PPRX because PBA reacts with a diol portion of the sugar molecule and forms a cyclic ester. When D-fructose or D-glucose was added to a suspension of PPRX, PPRX disintegrated, depending on the concentration of the sugars. Interestingly, catechol does not show a response although catechol has a high affinity for PBA. We analyzed the response mechanism of PPRX by considering equilibria.

Switchable glucose-responsive volume phase transition behavior of poly(phenylboronic acid) microgels

We report a poly(phenylboronic acid) microgel that can display switchable glucose-responsive volume phase transition behavior with temperature as a trigger.

Phenylboronic Acid-Installed Polycarbonates for the pH-Dependent Release of Diol-Containing Molecules

Environmental responsiveness is an appealing trait of emerging polymeric materials, as shown for a variety of pH-responsive drug delivery systems. The chemical versatility of the conjugation site and conjugate lability to physiologically relevant changes in pH will largely determine their applicability. Herein, we report on the use of a drug-polymer complex based on boronic acid-functionalized polycarbonates (PPBC) as the substrate for the pH-sensitive delivery of a diol-containing drug, capecitabine (CAPE). Complexation of CAPE with a PEGylated-PPBC block copolymer, via boronic ester formation, resulted in amphiphiles capable of self-assembling into spherical nanoparticles. We examined nanoparticle stability and release kinetics in neutral and acidic media and relate differences in release profiles and particle stability with changes to polymer chemistry. Comparison of complexed nanoparticles with their noncomplex analogues revealed striking differences in release rate and particle stability. Illustrated herein for capecitabine, the pH-sensitive dissociation of boronate esters from PPBCs can be applied in a general manner to diol- or catechol-containing solutes, demonstrating the utility of these polymers for biomedical applications.

Sensitive SERS glucose sensing in biological media using alkyne functionalized boronic acid on planar substrates

In this work, we propose a novel glucose binding mechanism on a highly sensitive SERS substrate, in order to overcome challenges in specific glucose detection in bio-fluids. We make use of phenylboronic acid as a receptor for saccharide capture onto the substrate and the ability of the captured glucose molecule to undergo secondary binding with an alkyne-functionalized boronic acid to form a glucose-alkyne-boronic acid complex. The formation of this complex shows high selectivity for glucose, over other saccharides. In addition, the alkyne group of the alkyne-functionalized boronic acid exhibits a distinct Raman peak at 1996 cm(-1) in a biological silent region (1800-2800 cm(-1)) where most endogenous molecules, including glucose, show no Raman scattering, thus offering a high sensitivity over other SERS glucose sensing. The substrate offers long-term stability, as well as high SERS enhancement to the glucose-alkyne boronic acid complex on substrate. In addition, the reversibility of SERS signals at various incubation stages also shows reusability capabilities, whereas positive results in clinical urine samples demonstrate clinical feasibility. All these strongly suggest that this newly developed SERS-based assay offers great potential in glucose sensing.

Detection and Monitoring of Microparticles Under Skin by Optical Coherence Tomography as an Approach to Continuous Glucose Sensing Using Implanted Retroreflectors

We demonstrate the feasibility of using optical coherence tomography (OCT) to image and detect 2.8 μm diameter microparticles (stationary and moving) on a highly-reflective gold surface both in clear media and under skin in vitro. The OCT intensity signal can clearly report the microparticle count, and the OCT response to the number of microparticles shows a good linearity. The detect ability of the intensity change (2.9% ± 0.5%) caused by an individual microparticle shows the high sensitivity of monitoring multiple particles using OCT. An optical sensing method based on this feasibility study is described for continuously measuring blood sugar levels in the subcutaneous tissue, and a molecular recognition unit is designed using competitive binding to modulate the number of bound microparticles as a function of glucose concentration. With further development, an ultra-small, implantable sensor might provide high specificity and sensitivity for long-term continuous monitoring of blood glucose concentration.

Ultrafast NMR T1 relaxation measurements: probing molecular properties in real time

The longitudinal relaxation properties of NMR active nuclei carry useful information about the site-specific chemical environments and about the mobility of molecular fragments. Molecular mobility is in turn a key parameter reporting both on stable properties, such as size, as well as on dynamic ones, such as transient interactions and irreversible aggregation. In order to fully investigate the latter, a fast sampling of the relaxation parameters of transiently formed molecular species may be needed. Nevertheless, the acquisition of longitudinal relaxation data is typically slow, being limited by the requirement that the time for which the nucleus relaxes be varied incrementally until a complete build-up curve is generated. Recently, a number of single-shot-inversion-recovery methods have been developed capable of alleviating this need; still, these may be challenged by either spectral resolution restrictions or when coping with very fast relaxing nuclei. Here, we present a new experiment to measure the T1s of multiple nuclear spins that experience fast longitudinal relaxation, while retaining full high-resolution chemical shift information. Good agreement is observed between T1s measured with conventional means and T1s measured using the new technique. The method is applied to the real-time investigation of the reaction between D-xylose and sodium borate, which is in turn elucidated with the aid of ancillary ultrafast and conventional 2D TOCSY measurements.