Fluorescent glucose biosensor

Fluorescent glucose biosensors are devices that measure the concentration of glucose in diabetic patients by means of sensitive protein that relays the concentration by means of fluorescence, an alternative to amperometric sension of glucose. Due to the prevalence of diabetes, it is the prime drive in the construction of fluorescent biosensors. A recent development has been approved by the FDA allowing a new continuous glucose monitoring system called EverSense, which is a 90 day glucose monitor using fluorescent biosensors. Fluorescent glucose biosensors are devices that measure the concentration of glucose in diabetic patients by means of sensitive protein that relays the concentration by means of fluorescence, an alternative to amperometric sension of glucose. Due to the prevalence of diabetes, it is the prime drive in the construction of fluorescent biosensors. A recent development has been approved by the FDA allowing a new continuous glucose monitoring system called EverSense, which is a 90 day glucose monitor using fluorescent biosensors. Keeping glucose levels in check is crucial to minimize the onset of the damage caused by diabetes. As a consequence, in conjunction with insulin administrations, the prime requirement for diabetic patients is to regularly monitor their blood glucose levels. The monitoring systems currently in general use have the drawback of below optimal number of readings, due to their reliance on a drop of fresh blood. Some continuous glucose monitors are commercially available, but suffer from the severe drawback of a short working life of the probe. The majority of these work amperometrically. As a result, there is an effort to create a sensor that relies on a different mechanism, such as via external infrared spectroscopy or via fluorescent biosensors. Various strategies exist to detect glucose levels using fluorescence, the first and most common being a .mw-parser-output .smallcaps{font-variant:small-caps}Fret competition assay between glucose and a labelled glucose polymer for the binding site of Concanavalin A.Over the years, using a combination of rational design and screening approaches, many possible combinations of fluorescent sensor for glucose have been studied with varying degrees of success: In most approaches, the glucose concentration is translated into a change in fluorescence either by using a Fret pair or by using environment sensitive (solvatochromic) dyes in a variety of combinations, the fluorescent small molecule, protein or quantum dot have been used in conjunction with a glucose binding moiety either a boronic acid functionalized fluorophore or a protein, such as glucose oxidase, concanavalin A, glucose/galactose-binding protein, glucose dehydrogenase and glucokinase.In general, the change seen with Fret competition assays is small (see below). Fluorescence is a property present in certain molecules, called fluorophores, in which they emit a photon shortly after absorbing one with a higher energy wavelength. To be more specific, in order for an electron in the outer orbital of a molecule to jump from a ground-state orbital to an excited state orbital, it requires a fixed amount of energy, which, in the case of chromophores (molecules that absorb light), can be acquired by absorbing a photon with an energy equal or slightly higher. This state is short-lived, and the electron returns to the ground-level orbital, losing the energy either as heat or in the case of fluorophores by emitting a photon, which, due to the loss of the difference between the energy of the absorbed photon and the excitation energy required, will have a lower energy than the absorbed photon, or, expressed in terms of wavelength, the emitted photon will have a longer wavelength. The difference between the two wavelengths is called Stokes’ shift. This property can be found in quantum dots, certain lanthanides and certain organic molecules with delocalized electrons. These excited molecules have an increase in dipole momentum and in some cases can undergo internal charge rearrangement. When they possess an electron withdrawing group and an electron donating group at opposite ends of the resonance structure, they have a large shift in charge distribution across the molecule, which causes the solvent molecules to reorient to a less energetic arrangement, called solvent relaxation. By doing so, the energy of the excited state decreases, and the extent of the difference in energy depends on the polarity of the solvent surrounding the molecule. An alternative approach is to use solvatochromic dyes, which change their properties (intensity, half-life, and excitation, and emission spectra), depending on the polarity and charge of their environments. Hence, they are sometimes loosely referred to as environmentally sensitive dyes. These can be positioned on specific residues that either change their spatial arrangement due to a conformational change induced by glucose or reside in the glucose-binding pocket whereby the displacement of the water present by glucose decreases the polarity. An additional property of fluorescence that has found a large usage is Förster resonance energy transfer (Fret) in which the energy of the excited electron of one fluorophore, called the donor, is passed on to a nearby acceptor dye, either a dark-quencher (non-emitting chromophore) or another fluorophore, which has an excitation spectrum that overlaps with the emission spectrum of the donor dye, resulting in a reduced fluorescence.