Harnessing a nanostructured fluorescence energy transfer sensor for quick detection of extremely small amounts of glucose

Carbon Nanostructure-Based DNA Sensor Used for Quickly Detecting Breast Cancer-Associated Genes

The early diagnosis of breast cancer highly relies on the detection of mutant DNA at low concentrations. Förster resonance energy transfer (FRET) quenching may offer a solution to quickly detect a small amount of single-strand DNA (ssDNA) through the combination of nanomaterials with special luminescence and unique structures of DNA double helix structure. Here, carbon quantum dots (CDs) modified with Capture ssDNA act as the FRET donor which interact with the two-dimensional fluorescence quencher, i.e., graphene oxide nanosheets (GO), to detect breast cancer-associated Target ssDNA at a low concentration. CDs bioconjugated with the designed Capture ssDNA (named CDs-Capture ssDNA) have the maximum fluorescence intensity (I_max) at the emission (λ_em) = 510 nm. The fluorescence of CDs-Capture ssDNA is quenched, while they interact with GO due to the π-π* interaction between ssDNA and GO. In the presence of Target ssDNA, the I_max is restored because of the stronger interaction between Target ssDNA and CDs-Capture ssDNA through the hydrogen bond. The restored fluorescence intensity of CDs has a linear relationship with the concentration of Target ssDNA from 0.25 to 2.5 μM with a detection limit around 0.24 μM. The selectivity of the sensing system has been further evaluated by testing the 3-base mismatched and non-base matched in which efficient restoration of photoluminescence of the sensing system cannot be observed. This carbon nanostructure-based DNA sensing system offers a user-friendly and quick detection of single-strand DNA at lower concentration.

Fluorescence Sensing Technologies for Ophthalmic Diagnosis

Personalized and point-of-care (POC) diagnoses are critical for ocular physiology and disease diagnosis. Real-time monitoring and continuous sampling abilities of tear fluid and user-friendliness have become the key characteristics for the applied ophthalmic techniques. Fluorescence technologies, as one of the most popular methods that can fulfill the requirements of clinical ophthalmic applications for optical sensing, have been raised and applied for tear sensing and diagnostic platforms in recent decades. Wearable sensors in this case have been increasingly developed for ocular diagnosis. Contact lenses, as one of the commercialized and popular tools for ocular dysfunction, have been developed as a platform for fluorescence sensing in tears diagnostics and real-time monitoring. Numbers of biochemical analytes have been examined through developed fluorescent contact lens sensors, including pH values, electrolytes, glucose, and enzymes. These sensors have been proven for monitoring ocular conditions, enhancing and detecting medical treatments, and tracking efficiency of related ophthalmic surgeries at POC settings. This review summarizes the applied ophthalmic fluorescence sensing technologies in tears for ocular diagnosis and monitoring. In addition, the cooperation of fabricated fluorescent sensor with mobile phone readout devices for diagnosing ocular diseases with specific biomarkers continuously is also discussed. Further perspectives for the developments and applications of fluorescent ocular sensing and diagnosing technologies are also provided.

Modern noninvasive methods for monitoring glucose levels in patients: a review

This paper presents the current state of the art of noninvasive glucose monitoring. In recent years, we can observe constant increase in the incidence of diabetes. About 40% of all performed blood tests apply to the glucose tests. Formerly, this lifestyle disease occurred mainly in rich countries, but now it is becoming more common in poorer countries. It is related to the increase in life expectancy, unhealthy diet, lack of exercise, and other factors. Untreated diabetes may cause many complications or even death. For this reason, daily control of glucose levels in people with this disorder is very important. Measurements with a traditional glucometer are connected with performing finger punctures several times a day, which is painful and uncomfortable for patients. Therefore, researches on other methods are ongoing. A method that would be fast, noninvasive and cheap could also enable testing the state of the entire population, which is necessary because of the number of people currently living with undiagnosed type 2 diabetes. Although the first glucometer was made in 1966, the first studies on glucose level measurement in tear film were documented as early as 1937. This shows how much a noninvasive method of diabetes control is needed. Since then, there have been more and more studies on alternative methods of glucose measurement, not only from tear fluid, but also from saliva, sweat, or transdermally.

Applications of mesoporous silica in biosensing and controlled release of insulin

The development of new oral insulin delivery systems could bring significant benefits to insulin-dependent patients due to the simplicity of the method, avoidance of pain caused by parenteral administration and maintenance of optimal therapeutic levels for a longer period. However, administration of such therapeutic proteins orally remains a challenge because insulin (Ins) is a very sensitive molecule and can be easily degraded under the existing pH conditions in the stomach and intestines. Moreover, due to the large size of insulin, intestinal epithelium permeability is very low. This could be improved by immobilizing insulin in the mesoporous silica pores (MSN), acting as a shield to protect the molecule integrity from the proteolytic degradation existing in the stomach and upper part of the small intestine. Due to the high adsorption capacity of insulin, biocompatibility, ease of functionalization with various organic and/or inorganic groups, high mechanical and chemical resistance, adjustable pore size and volume, MSN is considered an ideal candidate for the development of controlled release systems that are sensitive to various stimuli (pH, temperature) as well as to glucose. Modifying MSN surfaces by coating with various mucoadhesive polymers (chitosan, alginate, etc.) will also facilitate interaction with the intestinal mucus and improve intestinal retention time. Moreover, the development of glucose-responsive systems for achieving MSN-based self-regulated insulin delivery, decorated with various components serving as sensors - glucose oxidase (GOD_x) and phenylboronic acid (PBA) that can control the insulin dosage, avoiding overdose leading to serious hypoglycemia. MSN have also been tested for application as biosensors for glucose monitoring.

Fluorescent Nanobiosensors for Sensing Glucose

Glucose sensing in diabetes diagnosis and therapy is of great importance due to the prevalence of diabetes in the world. Furthermore, glucose sensing is also critical in the food and drug industries. Sensing glucose has been accomplished through various strategies, such as electrochemical or optical methods. Novel transducers made with nanomaterials that integrate fluorescent techniques have allowed for the development of advanced glucose sensors with superior sensitivity and convenience. In this review, glucose sensing by fluorescent nanobiosensor systems is discussed. Firstly, typical fluorescence emitting/interacting nanomaterials utilized in various glucose assays are discussed. Secondly, strategies for integrating fluorescent nanomaterials and biological sensing elements are reviewed and discussed. In summary, this review highlights the applicability of fluorescent nanomaterials, which makes them ideal for glucose sensing. Insight on the future direction of fluorescent nanobiosensor systems is also provided.

Nanostructured biosensor for detecting glucose in tear by applying fluorescence resonance energy transfer quenching mechanism

In this paper, a nanostructured biosensor is developed to detect glucose in tear by using fluorescence resonance energy transfer (FRET) quenching mechanism. The designed FRET pair, including the donor, CdSe/ZnS quantum dots (QDs), and the acceptor, dextran-binding malachite green (MG-dextran), was conjugated to concanavalin A (Con A), an enzyme with specific affinity to glucose. In the presence of glucose, the quenched emission of QDs through the FRET mechanism is restored by displacing the dextran from Con A. To have a dual-modulation sensor for convenient and accurate detection, the nanostructured FRET sensors were assembled onto a patterned ZnO nanorod array deposited on the synthetic silicone hydrogel. Consequently, the concentration of glucose detected by the patterned sensor can be converted to fluorescence spectra with high signal-to-noise ratio and calibrated image pixel value. The photoluminescence intensity of the patterned FRET sensor increases linearly with increasing concentration of glucose from 0.03mmol/L to 3mmol/L, which covers the range of tear glucose levels for both diabetics and healthy subjects. Meanwhile, the calibrated values of pixel intensities of the fluorescence images captured by a handhold fluorescence microscope increases with increasing glucose. Four male Sprague-Dawley rats with different blood glucose concentrations were utilized to demonstrate the quick response of the patterned FRET sensor to 2µL of tear samples.

Biophysical characterization of lectin–glycan interactions for therapeutics, vaccines and targeted drug-delivery

Lectin–glycan interactions play a role in biological processes, host–pathogen interactions and in disease. A more detailed understanding of these interactions is not only useful for the elucidation of their biological function but can also be applied in immunology, drug development and delivery and diagnostics. We review some commonly used biophysical techniques for studying lectin–glycan interactions; namely: frontal affinity chromatography, glycan/lectin microarray, surface plasmon resonance, electrochemical impedance spectroscopy, isothermal titration calorimetry, fluorescent assays, enzyme linked lectin sorbent assay and saturation transfer difference nuclear magnetic resonance spectroscopy. Each method is evaluated on efficiency, cost and throughput. We also consider the advantages and limitations of each technique and provide examples of their application in biology, drug discovery and delivery, immunology, glycoprofiling and biosensing.