This paper reports a flexible electronics-based epidermal biomicrofluidics technique for clinical continuous blood glucose monitoring, overcoming the drawback of the present wearables, unreliable measurements. A thermal activation method is proposed to improve the efficiency of transdermal interstitial fluid (ISF) extraction, enabling extraction with a low current density to notably reduce skin irritation. An Na+ sensor and a correction model are proposed to eliminate the effect of individual differences, which leads to fluctuations in the amount of ISF extraction. An electrochemical sensor with a 3D nanostructured working electrode surface is designed to enable precise in situ glucose measurement. A differential structure is proposed to eliminate the effect of passive perspiration, which leads to inaccurate blood glucose prediction. Fabrications of the epidermal biomicrofluidic device including formation of flexible electrodes, nanomaterial modification, and enzyme immobilization are fully realized by inkjet printing to enable facile manufacturing with low cost, which benefits practical production.
A novel flexible enzyme-electrode sensor was fabricated with a big cylindrical working electrode which, cooperating with the surface-modified 3D nanostructure, significantly improved the sensitivity.
This paper presents a continuous glucose monitoring microsystem consisting of a three-electrode electrochemical sensor integrated into a microfluidic chip. The microfluidic chip, which was used to transdermally extract and collect subcutaneous interstitial fluid, was fabricated from five polydimethylsiloxane layers using micromolding techniques. The electrochemical sensor was integrated into the chip for continuous detection of glucose. Specifically, a single-layer graphene and gold nanoparticles (AuNPs) were decorated onto the working electrode (WE) of the sensor to construct a composite nanostructured surface and improve the resolution of the glucose measurements. Graphene was transferred onto the WE surface to improve the electroactive nature of the electrode to enable measurements of low levels of glucose. The AuNPs were directly electrodeposited onto the graphene layer to improve the electron transfer rate from the activity center of the enzyme to the electrode to enhance the sensitivity of the sensor. Glucose oxidase (GOx) was immobilized onto the composite nanostructured surface to specifically detect glucose. The factors required for AuNPs deposition and GOx immobilization were also investigated, and the optimized parameters were obtained. The experimental results displayed that the proposed sensor could precisely measure glucose in the linear range from 0 to 162 mg/dl with a detection limit of 1.44 mg/dl (S/N = 3). The proposed sensor exhibited the potential to detect hypoglycemia which is still a major challenge for continuous glucose monitoring in clinics. Unlike implantable glucose sensors, the wearable device enabled external continuous monitoring of glucose without interference from foreign body reaction and bioelectricity.
This paper proposes
a novel strategy and an all-in-one toolbox
that allows instrument-free customization of integrated microfluidic
systems. Unlike the modular design of combining multiple microfluidic
chips in the previous literature, this work, for the first time, proposes
a “template sticker” method, in which sacrificial templates
for microfluidic components are batch-produced in the form of standardized
stickers and packaged into a toolbox. To create a customized monolithic
microfluidic system, the end users only need to select and combine
various template stickers following formulated steps. The fabricated
microfluidic devices have well-defined microscale features, while
the fabrication process is inexpensive and time-saving. Various functional
microfluidic devices were fabricated and tested using this toolbox.
The capability to create microchannels on curved surfaces is also
demonstrated. As a proof of concept, we developed with the proposed
toolbox a colorimetric testing platform for the detection of nitrite
ions. The sticker toolbox, as the first self-contained portable platform
for microfluidic fabrication, allows prompt customization of monolithic
devices, enabling deployment of microfluidics with both ideal performance
and customizability.
This paper presents a novel method of rapidly customizing
microfluidic
systems using a consumer-grade inkjet printer and a commercially available
superhydrophobic spray. By casting polydimethylsiloxane (PDMS) on
liquid templates that are defined by inkjet-printed hydrophilic patterns
on superhydrophobically-coated PDMS substrates, microfluidic devices
can be directly fabricated. Utilizing the interfacial properties of
the superhydrophobic coating and the template liquid, the fabrication
of microfluidics could be done with minimum effort and expertise,
and unlike previously reported works, no mask and bonding process
is necessary. As a proof of concept, we created different microfluidic
devices for various applications, like gradient generation and pneumatic
control of fluid. Appealing in its simplicity and rapidness, the newly
proposed technique could provide an easy-to-use microfluidic platform
for front-line researchers with different backgrounds to quickly customize
microfluidic devices.
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