A team of Caltech engineers has developed an ink-jet-printable bio-sensor for skin using designer nano-particles.
“Wearable biosensors that incorporate the nano-particles have been used to monitor metabolites in patients suffering from long covid, and the levels of chemotherapy drugs in cancer patients,” according to the university. “These sensors could be used to monitor a variety of biomarkers, such as vitamins, hormones, metabolites and medications in real time.”
The particles are cubic core-shell structures, formed in a solution that includes the molecule of interest – vitamin C, for example, said the university.
Monomers in the solution are chosen to spontaneously form into the polymer shell around the core of the structure, trapping molecules of vitamin C (in the example) in the shell layer.
A solvent is then used to remove the vitamin C, leaving the shell “dotted with holes that have shapes exactly matching that of the vitamin C molecules – akin to artificial antibodies that selectively recognise the shapes of only particular molecules”, said CalTech.
The tiny core (with shell, right) is made of nickel hexacyanoferrate, a material that can be oxidised or reduced by an applied voltage in the presence of an electrolyte – the sweat from skin, for example.
“This core is critical,” said medical engineering professor Wei Gao. “Nickel hexacyanoferrate is highly stable, even in biological fluids, making these sensors ideal for long-term measurement.”
However, fluids can only reach the core through the polymer shell while the vitamin C shaped pores are open.
Once exposed to sweat containing vitamin C, the pores block one vitamin molecule at a time, gradually electrically isolating the core. “The strength of the electrical signal reveals just how much vitamin C is present,” said Caltech.
The particles are designed to be ink-jet printable, and, along with vitamin C, inks with particles that sense kidney health marker creatinine and amino acid tryptophan were made for monitoring long-covid.
These three inks were printed into a single patch (inner trisected circle in the photos) on a flexible substrate, with carbon and gold inks used to form the other sensor electrodes.
Similarly, the researchers printed out nanoparticles-based wearable sensors that were specific to three different antitumor drugs on individual sensors that were then tested on cancer patients.
During the chemotherapy drug test “we were able to remotely monitor the amount of cancer drugs in the body at any given time”, said Gao.
Caltech worked with the Beckman Research Institute and UCLA.
The paper ‘Printable molecule-selective core–shell nanoparticles for wearable and implantable sensing‘ describes the research in Nature Materials – the abstract can be read without payment.
