The entire field of biomedical monitoring is one where flexible and ultra-thin electronic products will bring about huge changes. In the near future, we will see implantable sensors that are self-powered and can continuously monitor organ function and analyte levels in different body fluids.
Researchers in China have now demonstrated materials and technologies for highly sensitive flexible biosensors integrated with metal-organic frameworks (MOFs)-metal-organic frameworks are essentially inorganic-organic mixtures that contain repeated metal ions and organic ligands connection. These high-throughput flexible devices enable highly specific and sensitive electrochemical detection and can be used to monitor neurotransmitters and nutrients in the body.
The research team led by Professor Huang Xian of the Bio-Flexible Electronics and High-Throughput Measurement Technology Biomedical Engineering Laboratory of Tianjin University reported their findings in advanced materials ("Using flexible sensors with integrated metal organics for implantable nutrition transfer Sense of materials and technical framework").
Huang told Nanowerk: "This is the first time MOF has been integrated with flexible electronic devices." "This integration enables flexible electronic devices to perform electrochemical detection of nutrients without enzymes, and thus has new functions."
Schematic diagram of a flexible electrochemical sensor modified by MOF
Schematic diagram of a flexible electrochemical sensor modified by MOF. a) The concept of MOF improved flexible sensor for nutrition detection. b) Screen printing process of flexible sensors. c) The multilayer structure of the MOF electrochemical sensor, in which the MOFs layer is integrated. The left picture shows the scanning electron microscope (SEM) micrograph of Cu-MOF before grinding, and the right picture shows the 3D skeleton structure of Cu-MOF formed by hydrogen bonding. d) CV test of bare electrode and Cu-MOF modified electrode in PBS. (Reprinted with permission from Wiley-VCH Verlag) (click on the image to enlarge)
The ability of MOF in catalysis has been extensively studied. However, so far, there is no report on the application of MOF in flexible electronic products in the literature.
This inspired the team to explore the possibility of integrating MOF into their recently developed high-throughput flexible electrochemical sensors.
Huang said: “Although MOF has various demonstrations in chemical sensing, they have never been demonstrated in implantable biosensing and are integrated with flexible sensors for multi-channel determination of nutrition.”
There are two important findings of the team‘s work. First, it shows that MOF, which is essentially a brittle and rigid material, can be integrated with flexible electronic devices to achieve high-resolution, highly specific electrochemical detection.
Secondly, the results further indicate that flexible electronic devices can be used to monitor physiological signals in the body in a distributed manner.
The researchers fabricated their flexible sensors by screen printing methods. The device was surface-modified by a thin film made of ground copper-MOF (Cu-MOF) and cobalt-MOF (Co-MOF) nanoparticles.


Left: SEM micrograph of Cu-MOF nanoparticles on the electrode surface. Right: SEM cross-sectional view of Cu-MOF modified sensor. (Reprinted with permission from Wiley-VCH Verlag)
These sensors can be used to detect trace amounts of ascorbic acid, L-tryptophan, glycine, and glucose, all of which are nutrients closely related to metabolism and circulation processes.
The team proved that their sensors can work with a reduced bias voltage and extend the working time by 20 days. They also introduced preliminary data obtained through the use of bio-inspired tentacle-shaped multi-channel sensors, demonstrating the potential applications of such sensors in determining the distribution and transport of analytes in different organs and body positions simultaneously.
Because the MOF is very stable after implantation, the new technology may be used to simultaneously monitor biomolecules in different locations for a long time.
Huang said: "We plan to combine light and electrical stimulation, electrochemical detection and other physiological signal monitoring to build high-throughput, distributed flexible electronic devices as tools to reveal the complex mechanisms behind diseases and biological processes." "In addition , We will also take advantage of MOF in persistent phosphorescence, energy storage, etc. to further explore the application of MOF in flexible electronic products."
He added: "These devices can be used as tools to help better understand various life processes." "They can be used as implants to monitor biomolecules in different locations of various organs. When used with more stimulation and measurement When the functions are integrated, this type of device can be used to control the behavior of animals, reveal the underlying mechanisms of biological processes, monitor health and treat diseases."
Looking ahead, the team plans to introduce other rigid and brittle materials into flexible electronic devices to enhance the functionality of flexible electronic devices. Challenges include how to use rigid and brittle materials to obtain high-performance flexible membranes, and how to implement implantable complex flexible electronic systems with more functions.