Using a smartphone-based microscope to detect single molecules and detect diseases

Biomarkers play an important role in diagnosing a disease and evaluating its course. Symptoms now in use include genes, proteins, hormones, lipids and other classes of molecules. Biomarkers are found in the blood, in cerebrospinal fluid, urine and various types of faeces, but most of them have one thing in common: They occur in very low concentrations, so they are technically challenging. seek and measure.

Many detection methods use molecular probes, such as antibodies or short nucleic-acid sequences, that are designed to bind to specific biomarkers. When a probe recognizes and attaches to its target, a chemical or physical reaction causes fluorescence signals. Such methods work well, as long as they are sensitive enough to identify the relevant biomarker in a high percentage of all patients who carry it in their blood.

Furthermore, before such fluorescence-based experiments can be applied in practice, the biomarkers themselves or their signals must be augmented. The ultimate goal is to allow medical screening to be performed directly on patients, without sending the samples to a remote laboratory for analysis.

Molecular antennas increase fluorescence signals Philip Tinnefeld, who holds a Chair in Physical Chemistry at LMU, has developed a strategy for determining levels of biofuels present in low densities. He has been successful in attaching DNA probes to small particles of gold or silver. Pairs of dimers act as nano-antennas that amplify the fluorescence signals.

The trick works as follows: Interaction between the nanoparticles and incoming light waves amplifies the local electromagnetic fields, which in turn leads to a large increase in the magnitude of the fluorescence . In this way, bacteria containing antibiotic-resistant genes and even viruses can be specifically detected.

“DNA-based nano-antennas have been studied for the past few years,” said Kateryna Trofymchuk, co-author of the study. “But the manufacture of these nanostructures presents challenges.” Research group Philip Tinnefeld has now succeeded in more precisely aligning the parts of their nano-antennas, and in positioning the molecules. DNA that are the determinants of capture at the site of signal amplification. Together, these changes enable the fluorescence signal to be increased more efficiently.

Moreover, in the minuscule volume involved, which is ordered by zeptoliters (zeptoliter is equivalent to 10-21 liters), even more molecules can be captured.

The high level of positional control is made possible by DNA nanotechnology, which takes advantage of the structural properties of DNA to control the accumulation of all kinds of nanoscale materials – in very large numbers. “In one sample, we can produce billions of these nano-antennas, using an approach that basically incorporates a few solutions together,” Trofymchuk says.

Conventional diagnostics on the smartphone “In the future,” says Viktorija Glembockyte, who was also the first published author, “our technology could be used for diagnostic tests even in areas where access to electricity or laboratory equipment is restricted. We have shown that we can directly detect small pieces of DNA in a blood serum, using a portable, smartphone-based microscope that runs on a standard USB power pack to monitor the assessment. “

Newer smartphones are usually equipped with very good cameras. Plus, all you need is a laser and a lens – both easily accessible and inexpensive. LMU researchers used this basic recipe to build their prototypes.

They went on to prove that DNA fragments specific for antibiotic-resistant genes in bacteria could be detected by this establishment. But the assay could be easily modified to detect a whole range of interesting target types, such as viruses. Tinnefeld is optimistic: “The past year has shown that new and innovative diagnostic methods are always needed, and perhaps our technology can one day contribute to the development of a cheap and reliable diagnostic test that can be performed. at home. “