27 Jun 2023
Detection of wider concentration ranges could help transition into clinical use.
Achieving a wide dynamic range in these devices has remained a challenge, however, usually imposing compromises in sensor performance and complexity, or requiring different detection modalities to observe different molecules.
As a result most such sensors are designed for just one target or only able to test a narrow range of concentrations, an unhelpful restriction when the concentrations of proteins used as disease biomarkers can vary by several orders of magnitude.
A project at the University of California, Santa Cruz (UCSC) has now demonstrated a new approach for multiplex detection of fluorescent targets across a wide range of concentration scales. The work was published in Optica.
"This work is our latest step in developing integrated optofluidic sensing devices that are sensitive enough to detect single biomolecules and work over a very wide range of concentrations," said Holger Schmidt from UCSC's W.M. Keck Center for Nanoscale Optofluidics.
"We have shown that this can be done with a single method, which allows us to simultaneously measure and distinguish multiple particle types at once even if they have very different concentrations."
The new work builds on previous UCSC research into how one sensor might detect multiple types of nucleic acids, proteins, viruses, bacteria and cancer biomarkers. Until now this has been achieved with separate detectors and signal analysis techniques to measure different concentrations, to avoid the larger signal from high-concentration species overwhelming the smaller response from other, sparsely present, targets.
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The answer involved applying signal processing methods that can detect particles in both high and low concentrations simultaneously even if the concentrations are not known in advance. This in turn required a combination of signal modulation frequencies.
High frequency laser modulation can distinguish single particles at low concentrations, while low frequency laser modulation can detect large signals from many particles simultaneously at high concentrations.
"Additionally we implemented a feedback loop that detects when signals are really large and adjusts the input laser power accordingly," said Schmidt. "In this way, we can detect large signals from high concentrations without overwhelming the weak signals that may be present from another species at low concentrations. This allowed us to simultaneously detect particles that were present in very different concentrations."
A further step was to apply an algorithm developed to identify single particle signals at low concentrations in real time. Machine learning also helped with recognizing signal patterns so that different particle types could be distinguished with high accuracy.
"These signal analysis advances are ideal for enabling device operation at the point of care, where signal quality can be poor and where data analysis is required in real time," Schmidt noted.
In proof-of-concept trials, optofluidic biosensor chips were pumped with a solution of nanobeads at different concentrations and with various fluorescence colors. The new approach was able to correctly identify the concentration of both yellow-green and crimson beads, when those concentrations in the mixture differed by a factor of more than 10,000.
The new optofluidic biosensing technology is currently being commercialized by medical device developer Fluxus, originally a UCSC spin-out but since November 2022 a subsidiary of Japan's Fujirebio biotech company.
UCSC is now working to adapt its method to the study of molecular products from artificial neuronal cell tissue organoids, along with potential use in point-of-care applications, study of neurogenerative disease or treatment of pediatric cancer.