Utilizing a cell phone based microscope for recognizing single molecules and diagnosing infections

Overview

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• Source: Ludwig-Maximilians-Universität München


• Date: 14 Feb,2021

Biomarkers play a central role in the identification of disease and evaluation of its course. Among the markers now in use are genes, hormones, proteins, lipids and other types of molecules. Biomarkers can be found in the bloodstream, in cerebrospinal fluid, urine and various types of tissues, but many of them have one thing in common: They occur in extremely low concentrations, and are therefore technically hard to detect and measure.

Many detection procedures utilize molecular probes, such as antibodies or short nucleic-acid sequences, which are designed to bind to specific biomarkers. When a probe recognizes and binds to its target, physical or chemical reactions contribute to fluorescence signals. Such methods work well, provided they are sensitive enough to comprehend the relevant biomarker in a high proportion of patients who take it in their blood.

Additionally, before such fluorescence-based tests may be utilised in practice, the biomarkers their signals must be amplified. The ultimate purpose is to empower medical screening to be carried out directly on patients, without needing to send the samples to a remote laboratory for analysis.

Molecular antennas amplify fluorescence signals Philip Tinnefeld, who holds a Chair in Physical Chemistry at LMU, has developed a strategy for determining levels of biomarkers present in low concentrations. He has succeeded in coupling DNA probes to tiny particles of silver or gold.

The trick works as follows: Interactions between the nanoparticles and incoming light waves intensify the local electromagnetic fields, which in turn leads to a enormous increase in the amplitude of the fluorescence. In this way, bacteria which contain antibiotic resistance genes and even viruses could be specifically detected.

“DNA-based nano-antennas have been studied for the last couple of years,” states Kateryna Trofymchuk, joint first author of the study. “But the manufacture of these nanostructures presents challenges.” Philip Tinnefeld’s research group has succeeded in configuring the components of their nano-antennas more precisely, and in positioning the DNA molecules that function as capture probes at the website of signal amplification. Together, these modifications permit the fluorescence signal to be effectively amplified.

Moreover, in the minuscule volume involved, which can be on the order of zeptoliters (a zeptoliter equals 10-21 of a liter), more molecules can be recorded.

The high level of positioning control is made possible by DNA nanotechnology, which exploits the structural properties of DNA to direct the assembly of all sorts of nanoscale objects – in extremely large numbers. “In one sample, we could simultaneously produce countless these nano-antennas, using a procedure that essentially consists of pipetting a few solutions together,” states Trofymchuk.

Regular diagnostics on the smartphone”In the long run,” says Viktorija Glembockyte, also joint first author of the publication,”our technology could be used for diagnostic tests even in areas in which access to electricity or laboratory equipment is restricted. We’ve proven that we could directly detect little fragments of DNA in blood serum, with a portable, smartphone-based microscope that runs on a traditional USB power pack to monitor the assay.”

Newer smartphones are often equipped with pretty good cameras. Besides that, all that’s needed is a laser and a lens – two readily available and affordable components. The LMU researchers used this basic recipe to construct their prototypes.

But the assay could be easily modified to detect a whole selection of interesting target types, like viruses. Tinnefeld is optimistic:”The past year has revealed that there is always a demand for new and advanced diagnostic methods, and possibly our technology can one day contribute to the development of an affordable and reliable diagnostic test that may be performed at home.”