Existing techniques of continuous glucose monitoring for diabetics at home have traded accuracy in favor of greater use, reduced cost, and portability. A group of scientists have created a biosensor for such monitors using “zero-dimensional” quantum dots (QDs) and gold nanospheres (AuNSs), eliminating the need for a trade-off in precision.
The improved biosensor design was published in the journal Nano Research on November 9, 2022.
Diabetes patients have benefited greatly from the recent introduction of CGM technology. Improvements in diabetes management can be attributed in large part to the real-time, quick, and precise detection of glucose levels provided by always-on CGM systems as opposed to pre-meal and pre-bedtime blood sugar tests.
Alarms are sent to the individual, their parents, partners, or caregivers when glucose levels rise too high or fall too low, and glucose trends may be followed more readily, making it easier to adopt adjustments in food, exercise, and medication as part of a diabetic care plan throughout the day.
Clinical glucose monitors (CGMs) primarily function by measuring glucose levels in the fluid between cells. This sensor performs regular checks of these levels and reports its findings on a screen. The insulin pump can also be linked to the monitor.
Colorimetry, infrared spectroscopy, fluorescence spectroscopy, and mass spectrometry are only a few of the methods that have been developed for glucose detection. Electrochemical glucose detection is the most frequently recognized method because of its quick reaction, ease of use, low cost, and portability, making it well-suited for usage in a home setting rather than a clinic or hospital.
Microelectronics expert Huan Liu from Huazhong University of Science & Technology’s School of Optical and Electronic Information stated that it also has acceptable sensitivity, but not great sensitivity. Not when compared to other methods employed in the medical field. As a result, they were interested in seeing if they might increase that sensitivity and therefore enhance its precision.
Both enzyme-based and non-enzyme-based electrochemical glucose sensors exist. In order to oxidize glucose on the surface of the CGM sensor electrode, glucose oxidase (GOx) is commonly utilized. This enzyme speeds up (catalyzes) oxidation-reduction chemical processes.
Attracting electrons from the glucose and oxidizing it causes the electrode to produce an electric current whose strength is proportional to the glucose concentration. Since GOx is highly active, stable, and selective for glucose over a broad pH range, it is frequently employed for this purpose.
Unfortunately, the biological activity and stability of GOx can be compromised when it is mixed directly with the bare electrode surface, since GOx is quickly exfoliated (stripped of part of its layers). Furthermore, the sensitivity of the sensor is largely determined by the efficiency of electron transport between the GOx and the electrode surface.
To improve the efficiency of electron transfer between the electroactive centers (sites of electron activity) and the electrode surface, many methods have been tried to improve the GOx enzyme’s affinity for the latter. In one promising effort, nanoscale patterns on electrodes are used to boost electrocatalytic activity and increase surface area.
The complexity of making electrochemical biosensors is increased, however, by the presence of nanostructures. The synthetic polymer Nafion is used as a framework in their construction, acting as a barrier to charge transfer between the sensor and the fluid under investigation.
As a result, the research team has shifted gears. The group decided to use colloidal quantum dots (CQDs) to alter the electrode in an effort to boost glucose sensing capability. Nanoparticle semiconductors with “zero” dimensions, also known as CQDs. (They don’t have zero dimensions; rather, they have incredibly small diameters, usually between 2 and 20 nm). They attach tightly to protein molecules and feature a high density of active sites, or areas at which chemical reactions can take place.
And since CQDs are so small, quantum processes like quantum tunneling can occur, and an external electric field can be used to control the charge transfer at the CQD-protein interface. Since CQDs can work with both rigid and flexible substrates, they are also simpler to produce.
Researchers amplified this effect by including gold nanospheres (AuNSs) into the sensor electrode’s design. These nanoparticles have sizes of only 10–200 nm and are perfectly round. Because of their exceptional physical and chemical characteristics, they are finding increasing utility in biosensing applications.
For instance, AuNSs allow protein enzymes to keep their biological activity following attachment to surfaces and lessen the insulating effect of the shell of the protein for direct electron transfer when utilized as a component in enzymatic electrochemical biosensors. When used in a CGM, this significantly boosts the strength of the electrochemical biosensors’ output signals.
Using lead sulfide CQDs and the AuNSs-modified electrode, the researchers built a proof-of-concept CGM. They discovered that the current signal picked up by the electrochemical sensor was much enhanced by the presence of the AuNSs, as had been expected.
Collectively, these adjustments demonstrated considerable promise in detecting glucose in a variety of samples, including blood, sweat, and other bodily fluids, and delivered a rapid (in less than 30 seconds) electrochemical biosensor, with a broad detection range and the kind of ultra-high sensitivity the team had been after.
The team’s next step is to take the CGM they’ve developed as proof of concept and make it suitable for mass production.
Yunong Zhao et al. (2022). Electrochemical biosensor employing PbS colloidal quantum dots/Au nanospheres-modified electrode for ultrasensitive glucose detection, Nano Research. DOI: 10.1007/s12274-022-5138-0