Non-Invasive Blood Glucose Monitoring Technology: A Review.

In recent years, with the rise of global diabetes, a growing number of subjects are suffering from pain and infections caused by the invasive nature of mainstream commercial glucose meters. Non-invasive blood glucose monitoring technology has become an international research topic and a new method which could bring relief to a vast number of patients. This paper reviews the research progress and major challenges of non-invasive blood glucose detection technology in recent years, and divides it into three categories: optics, microwave and electrochemistry, based on the detection principle. The technology covers medical, materials, optics, electromagnetic wave, chemistry, biology, computational science and other related fields. The advantages and limitations of non-invasive and invasive technologies as well as electrochemistry and optics in non-invasives are compared horizontally in this paper. In addition, the current research achievements and limitations of non-invasive electrochemical glucose sensing systems in continuous monitoring, point-of-care and clinical settings are highlighted, so as to discuss the development tendency in future research. With the rapid development of wearable technology and transdermal biosensors, non-invasive blood glucose monitoring will become more efficient, affordable, robust, and more competitive on the market.

A Flexible Interdigital Electrode Used in Skin Penetration Promotion and Evaluation with Electroporation and Reverse Iontophoresis Synergistically.

Skin penetration is related to efficiencies of drug delivery or ISF extraction. Normally, the macro-electrode is employed in skin permeability promotion and evaluation, which has the disadvantages of easily causing skin damage when using electroporation or reverse iontophoresis by alone; furthermore, it has large measurement error, low sensitivity, and difficulty in integration. To resolve these issues, this paper presents a flexible interdigital microelectrode for evaluating skin penetration by sensing impedance and a method of synergistical combination of electroporation and reverse iontophoresis to promote skin penetration. First, a flexible interdigital microelectrode was designed with a minimal configuration circuit of electroporation and reverse iontophoresis for future wearable application. Due to the variation of the skin impedance correlated with many factors, relative changes of it were recorded at the end of supply, different voltage, or constant current, times, and duration. It is found that the better results can be obtained by using electroporation for 5 min then reverse iontophoresis for 12 min. By synergistically using electroporation and reverse iontophoresis, the penetration of skin is promoted. The results tested in vivo suggest that the developed microelectrode can be applied to evaluate and promote the skin penetration and the designed method promises to leave the skin without damage. The electrode and the method may be beneficial for designing noninvasive glucose sensors.

Development of carbon-graphene-based aptamer biosensor for EN2 protein detection.

In this study, we developed a screen-printed carbon-graphene-based electrochemical biosensor for EN2 protein detection. The engrailed-2 (EN2) protein, a biomarker for prostate cancer, is known to be a strong binder to a specific DNA sequence (5'-TAATTA-3') to regulate transcription. To take advantage of this intrinsic property, aptamer probes with TAATTA sequence was immobilized onto the screen-printed carbon-graphene electrode surface via EDC-NHS coupling approach. Cyclic voltammetry (CV) of the electrochemical measurement technique was employed for the quantitative detection of EN2 protein. The hindrance to the redox reaction of potassium ferricyanide on the biosensor surface due to the binding of the immobilized aptamer with its target EN2 protein quantified the protein concentration. Under optimum conditions, the aptamer biosensor can detect EN2 protein over a linear range from 35 to 185 nM with a detection limit of 38.5 nM.

Micro interstitial fluid extraction and detection device integrated with the optimal extraction conditions for noninvasive glucose monitoring.

Interstitial fluid glucose sensors have promising prospects in noninvasive glucose monitoring. However, the commonly used method of extracting interstitial fluid, reverse iontophoresis (RI), still remains to be optimized to solve problems such as insufficient extraction flux and skin irritation. To find the optimal RI conditions, in this study we explored the effects of multiple factors such as current frequency, duration, duty cycle and their interactions on extraction with the design of experiments (DOE) method. A multifunctional extraction and detection device was designed to control extraction conditions and measure the surface water content of the extraction electrode in situ and real time. A micro glucose monitoring device (MicroTED) combined with a cheap and flexible paper-based electrode was developed under the determined optimal extraction conditions. In on-body continuous glucose monitoring tests carried out to verify the performance of the device, the optimized conditions can facilitate stable extraction of up to 1.0 mg without any skin discomfort. The mean Pearson correlation coefficient between the measurement results of MicroTED and commercial glucometer is above 0.9. In the Clarke error grid analysis, all data points fell within Clarke error grid areas A and B, demonstrating the feasibility of further clinical application of the device.

Application of chitosan with different molecular weights in cartilage tissue engineering.

Cartilage tissue engineering involves the invention of novel implantable cartilage replacement materials to help heal cartilage injuries that do not heal themselves, aiming to overcome the shortcomings of current clinical cartilage treatments. Chitosan has been widely used in cartilage tissue engineering because of its similar structure to glycine aminoglycan, which is widely distributed in connective tissues. The molecular weight, as an important structural parameter of chitosan, affects not only the method of chitosan composite scaffold preparation but also the effect on cartilage tissue healing. Thus, this review identifies methods for the preparation of chitosan composite scaffolds with low, medium and high molecular weights, as well as a range of chitosan molecular weights appropriate for cartilage tissue repair, by summarizing the application of different molecular weights of chitosan in cartilage repair in recent years.

Analyzation of the binding mechanism and the isoelectric point of glycated albumin with self-assembled, aptamer-conjugated films by using surface plasmon resonance.

Glycated albumin(GA), a biomarker which has great potential to replace glycated hemoglobin in the diagnosis and treatment of diabetes, is being extensively studied by scientists, especially in preventive medicine. Aptamers, as novel probes, have attracted much attention due to their high specificity, wide storage conditions, and simple preparation. However, the interaction mechanism between GA and its aptamer is still unclear, hindering the progress of diabetic aptamer sensors into clinical testing. In this study, the interaction mechanism between GA and its aptamer was evaluated for the first time using surface plasmon resonance by changing the pH value, salt concentration and temperature. The successful preparation of the sensor chip is proved by the water contact angle, Atomic Force Microscope, and the X-ray photoelectron spectroscopy. This study shows that the pH can greatly affect the formation of a complex from the interaction between the aptamer and GA. The interaction mechanism between GA aptamer and GA was caused by electrostatic force. Otherwise, this is the first time to detect protein isoelectric point (pI) using SPR. This study provides an important reference for researchers of aptamer sensors from the perspective of detection environment, and promotes the use of aptamer sensors to the clinic.

The Treatment of Keloid Scars via Modulating Heterogeneous Gelatin-Structured Composite Microneedles to Control Transdermal Dual-Drug Release.

Keloid scarring is an abnormal scar disease characterised by excessive proliferation of fibroblasts and over-deposition of collagen during wound healing. Although various treatments for keloid scars have been developed, preventive medicine is believed to be a promising strategy. The skin barrier limits the gentle topical administration of medicaments such as creams and hydrogel dressings, resulting in reduced therapeutic efficacy. In recent years, microneedles (MNs) have been regarded as an appreciable device for topical administration without inducing side effects, and they are painless and do not cause bleeding. In this study, an MN patch with controlled transdermal dual-drug release was developed to achieve combinatory treatment of keloid scars using a heterogeneous gelatin-structured composite MN. Gelatin hydrogel was used as a substrate to load gallic acid (GA) and quercetin-loaded amphiphilic gelatin nanoparticles to fabricate dual-drug heterogeneous composite MNs. The results of the insertion test and mechanical properties of the MNs showed that the heterogeneous composite MN patches could be self-pressed into the stratum corneum and control dual-drug release at different time periods. GA was released at an earlier stage to retard the proliferation of fibroblasts, and quercetin was released at a later stage as a strong antioxidant to erase the generation of reactive oxygen species. Furthermore, real-time quantitative polymerase chain reaction data indicated that the gene expression of fibroblasts (such as Col I and III) was downregulated in the dual-drug system. The above results demonstrate that using heterogeneous composite MNs with the combination of dual-drug pharmacology is beneficial for preventing keloid scar formation.

High-Density Horizontal Stacking of Chondrocytes via the Synergy of Biocompatible Magnetic Gelatin Nanocarriers and Internal Magnetic Navigation for Enhancing Cartilage Repair.

Osteoarthritis (OA) is a globally occurring articular cartilage degeneration disease that adversely affects both the physical and mental well-being of the patient, including limited mobility. One major pathological characteristic of OA is primarily related to articular cartilage defects resulting from abrasion and catabolic and proinflammatory mediators in OA joints. Although cell therapy has hitherto been regarded as a promising treatment for OA, the therapeutic effects did not meet expectations due to the outflow of implanted cells. Here, we aimed to explore the repair effect of magnetized chondrocytes using magnetic amphiphilic-gelatin nanocarrier (MAGNC) to enhance cellular anchored efficiency and cellular magnetic guidance (MG) toward the superficial zone of damaged cartilage. The results of in vitro experiments showed that magnetized chondrocytes could be rapidly guided along the magnetic force line to form cellular amassment. Furthermore, the Arg-Gly-Asp (RGD) motif of gelatin in MAGNC could integrate the interaction among cells to form cellular stacking. In addition, MAGNCs upregulated the gene expression of collagen II (Col II), aggrecan, and downregulated that of collagen I (Col I) to reduce cell dedifferentiation. In animal models, the magnetized chondrocytes can be guided into the superficial zone with the interaction between the internal magnetic field and MAGNC to form cellular stacking. In vivo results showed that the intensity of N-sulfated-glycosaminoglycans (sGAG) and Col II in the group of magnetized cells with magnetic guiding was higher than that in the other groups. Furthermore, smooth closure of OA cartilage defects was observed in the superficial zone after 8 weeks of implantation. The study revealed the significant potential of MAGNC in promoting the high-density stacking of chondrocytes into the cartilage surface and retaining the biological functions of implanted chondrocytes for OA cartilage repair.

A guided mode resonance aptasensor for thrombin detection.

Recent developments in aptamers have led to their widespread use in analytical and diagnostic applications, particularly for biosensing. Previous studies have combined aptamers as ligands with various sensors for numerous applications. However, merging the aptamer developments with guided mode resonance (GMR) devices has not been attempted. This study reports an aptasensor based home built GMR device. The 29-mer thrombin aptamer was immobilized on the surface of a GMR device as a recognizing ligand for thrombin detection. The sensitivity reported in this first trial study is 0.04 nm/µM for thrombin detection in the concentration range from 0.25 to 1 µM and the limit of detection (LOD) is 0.19 µM. Furthermore, the binding affinity constant (Ka) measured is in the range of 10(6) M(-1). The investigation has demonstrated that such a GMR aptasensor has the required sensitivity for the real time, label-free, in situ detection of thrombin and provides kinetic information related to the binding.

Investigation of the recognition interaction between glycated hemoglobin and its aptamer by using surface plasmon resonance.

Glycated hemoglobin (HbA1c) has been widely explored as an important marker for monitoring and diagnosing diabetes. Due to the advantages of high selectivity, easy preparation, and convenient preservation of aptamers, research on glycated hemoglobin detection utilizing aptasensors has received much attention in recent years. However, factors such as the pH and the salt concentration of the solution and the structure of the aptamer could influence the interactions between HbA1c and the aptamer. In this study, the factors were evaluated using surface plasmon resonance (SPR). The results show that the pH and the salt concentration can greatly affect the formation of a complex between the aptamer and HbA1c. In the stereostructure of the aptamer, loop L1 may be an important motif for recognizing glycated hemoglobin. In addition, the best condition for detecting HbA1c was at pH 6, with a high sensitivity and a low limit of detection(LOD) (1.06 × 10-3RUnM /2.55 nM). The results also demonstrated that the use of an SPR aptamer biosensor can be a sensitive technique to improve the accuracy and correctness of HbA1c measurement.

A Facile Fabrication of Biodegradable and Biocompatible Cross-Linked Gelatin as Screen Printing Substrates.

This study focuses on preparation and valuation of the biodegradable, native, and modified gelatin film as screen-printing substrates. Modified gelatin film was prepared by crosslinking with various crosslinking agents and the electrode array was designed by screen-printing. It was observed that the swelling ratio of C-2, crosslinked with glutaraldehyde and EDC/NHS (1-ethyl-3-(3-dimethylaminopropyl) carbodiimide/N-hydroxysuccinimide) was found to be lower (3.98%) than that of C-1 (crosslinked with only glutaraldehyde) (8.77%) and C-0 (without crosslinking) (28.15%). The obtained results indicate that the swelling ratios of both C-1 and C-2 were found to be lower than that of C-0 (control one without crosslinking). The Young's modulus for C-1 and C-2 was found to be 8.55 ± 0.57 and 23.72 ± 2.04 kPa, respectively. Hence, it was conveyed that the mechanical strength of C-2 was found to be two times higher than that of C-l, suggesting that the mechanical strength was enhanced upon dual crosslinking in this study also. The adhesion study indicates that silver ink adhesion on the gelation surface is better than that of carbon ink. In addition, the electrical response of C-2 with a screen-printed electrode (SPE) was found to be the same as the commercial polycarbonate (PC) substrate. The result of MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) assay suggested that the silver SPE on C-2 was non-cytotoxic toward L929 fibroblast cells proliferation. The results indicated that C-2 gelatin is a promising material to act as a screen-printing substrate with excellent biodegradable and biocompatible properties.

Screen-printed carbon electrode-based electrochemical immunosensor for rapid detection of microalbuminuria.

A urinary microalbumin test is used to detect early signs of kidney damage in people who have a risk of chronic kidney disease, such as those with diabetes or hypertension. In this study, we developed a screen-printed carbon electrode-based immunosensor for the detection of microalbumin in urine. Anti-human albumin antibodies were immobilized on the screen-printed sensor surface by the covalent immobilization method. Cyclic voltammetry (CV) and scanning electron microscopy with an energy dispersive spectroscopical (SEM-EDS) analysis demonstrated that the modification process was well performed. Chronoamperometric (CA) electrochemical measurement technique was employed for the quantitative detection of albumin. The electrochemical measurements performed with some possible interfering compounds normally present in urine (ascorbic acid, uric acid, glucose and creatinine samples) demonstrated a high specificity and selectivity of this immunosensor in albumin detection. Under optimum conditions, the immunosensor can detect urinary albumin in a wide linear range from 10 µg/ml to 300 µg/ml with a detection limit of 9.7 µg/ml. The excellent performance of this immunosensor was confirmed by analyzing microalbumin in urine samples; the results were in good agreement with those obtained by the standard immunoturbidimetric method. The biosensor proposed herein is easy to prepare and can be used for low-cost, rapid, and sensitive screening of microalbuminuria. This approach provides a promising platform for developing clinical point-of-care diagnostic applications.

In Situ Reductive Synthesis of Structural Supported Gold Nanorods in Porous Silicon Particles for Multifunctional Nanovectors.

Porous silicon nanodisks (PSD) were fabricated by the combination of photolithography and electrochemical etching of silicon. By using PSD as a reducing agent, gold nanorods (AuNR) were in situ synthesized in the nanopores of PSD, forming PSD-supported-AuNR (PSD/AuNR) hybrid particles. The formation mechanism of AuNR in porous silicon (pSi) was revealed by exploring the role of pSi reducibility and each chemical in the reaction. With the PSD support, AuNR exhibited a stable morphology without toxic surface ligands (CTAB). The PSD/AuNR hybrid particles showed enhanced plasmonic property compared to free AuNR. Because high-density "hot spots" can be generated by controlling the distribution of AuNR supported in PSD, surface-enhanced raman scattering (SERS) using PSD/AuNR as particle substrates was demonstrated. A multifunctional vector, PSD/AuNR/DOX, composed of doxorubicin (DOX)-loaded PSD/AuNR capped with agarose (agar), was developed for highly efficient, combinatorial cancer treatment. Their therapeutic efficacy was examined using two pancreatic cancer cell lines, PANC-1 and MIA PaCa-2. PSD/AuNR/DOX (20 µg Au and 1.25 µg DOX/mL) effectively destroyed these cells under near-IR laser irradiation (810 nm, 15 J·cm(-2) power, 90 s). Overall, we envision that PSD/AuNR may be a promising injectable, multifunctional nanovector for biomedical application.

Impedimetric method for measuring ultra-low E. coli concentrations in human urine.

In this study, we developed an interdigitated gold microelectrode-based impedance sensor to detect Escherichia coli (E. coli) in human urine samples for urinary tract infection (UTI) diagnosis. E. coli growth in human urine samples was successfully monitored during a 12-h culture, and the results showed that the maximum relative changes could be measured at 10Hz. An equivalent electrical circuit model was used for evaluating the variations in impedance characteristics of bacterial growth. The equivalent circuit analysis indicated that the change in impedance values at low frequencies was caused by double layer capacitance due to bacterial attachment and formation of biofilm on electrode surface in urine. A linear relationship between the impedance change and initial E. coli concentration was obtained with the coefficient of determination R(2)>0.90 at various growth times of 1, 3, 5, 7, 9 and 12h in urine. Thus our sensor is capable of detecting a wide range of E. coli concentration, 7×10(0) to 7×10(8) cells/ml, in urine samples with high sensitivity.

Resonant efficiency improvement design of piezoelectric biosensor for bacteria gravimetric sensing.

The piezoelectric biosensor have been widely used in ultra-small mass detection of biomolecular, based on PZT piezoelectric material can create a variety of compositions geometrically; it could widely develop a high-frequency resonator and measure the change of the slightest mass while improve the limited detection simultaneously. Therefore, the piezoelectric biosensor of this study was fabricated by a spin-coating method and backside etching process for improving the characteristic of piezoelectric biosensor. The result exhibited that the 250 µm × 250 µm working size has the most favorable piezoelectric characteristic. The tunability was approximately 38.56 % and it showed that reducing the substrate thickness could obtain a clear resonance signal in a range of 60 to 380 MHz. In theory calculated for gravimetric sensing, it could achieve 0.1 ng sensing sensitivity. In gravimetric sensing, the sensing range was between 50,000~100,000 CFU/ml. Sensing range was lower in clinical urinary tract infection (100,000 CFU/ml), thus demonstrating its usefulness for preventive medicine. It can understand the piezoelectric sensor of this study has potential application in the future for biomedical gravimetric sensing.

Concept for E.coli detection using interdigitated microelectrode impedance sensor.

This paper presents the concept to detect Escherichia coli O157:H7 based on electrochemical impedance spectroscopy at interdigitated microelectrode. Interdigitated microelectrode structures was designed and fabricated, with glass as substrate material and gold electrodes. The performance of the sensors was studied by measuring the capacitance in air and impedance spectra in DI water. The feasibility of the fabricated sensor for detecting different concentrations of Escherichia coli in water was demonstrated. Electrochemical impedance spectroscopy (EIS) was employed as the detection technique. The impedance based response significant change for different E.coli concentrations in the frequency range between 1 kHz to 100 kHz.

Surface plasmon resonance biosensor with high anti-fouling ability for the detection of cardiac marker troponin T.

Designing a surface recognition layer with high anti-fouling ability, high affinity, and high specificity is an important issue to produce high sensitivity biosensing transducers. In this study, a self-assembled monolayer (SAM) consisting of a homogeneous mixture of oligo(ethylene glycol) (OEG)-terminated alkanethiolate and mercaptohexadecanoic acid (MHDA) on Au was employed for immobilizing troponin T antibody and applied in detecting cardiac troponin T by using surface plasmon resonance (SPR). The mixed SAM showed no phase segregation and exhibited human serum albumin resistance, particularly with an antibody-immobilized surface. X-ray photoemission spectra revealed that the chemical composition ratio of OEG to the mixed SAM was 69% and the OEG packing density was 82%. The specific binding of troponin T on the designed surface indicated a good linear correlation (R=0.991, P<0.0009) at concentrations lower than 50 µgmL(-1) with the limit of detection of 100 ngmL(-1) using a SPR measuring instrument. It is concluded that the mixed SAM functions as designed since it has high detection capability, high accuracy and reproducibility, as well as shows strong potential to be applied in rapid clinical diagnosis for label-free detection within 2 min.

The investigation of recognition interaction between phenylboronate monolayer and glycated hemoglobin using surface plasmon resonance.

Glycated hemoglobin (HbA1c) is formed by a nonenzymatic reaction of glucose with the N-terminal valine of adult hemoglobin's beta-chain. The amount of HbA1c reflects the average concentration of glucose variation level over the preceding 2 to 3 months. Because the boronate has antibody mimicking for HbA1c, often it is used to detect HbA1c. However, factors such as the ratio of the phenylboronic acid derivatives and diol composition, the pH of the solution, and the stereostructure of phenylboronic acid derivatives could influence the interactions between phenylboronic acid derivatives and diol composition. In this study, the factors were evaluated using surface plasmon resonance (SPR). The results show that pH value is an important factor affecting HbA1c and phenylboronic acid to form the complex and Lewis bases. This could change the stereostructure of phenylboronic acid to form B(OH)(3) for binding with saccharine easily. In addition, linear response appeared in HbA1c in the range of 0.43 to 3.49 mug/ml, and the detection limit was 0.01 microg/ml. The results also demonstrated that an SPR biosensor can be used as a sensitive technique for improving the accuracy and correctness of HbA1c measurement.