- Researchers build a new technique to identify single proteins within minutes, using off-the-shelf components.
- It is 1000x more sensitive and significantly less expensive than the existing state-of-the-art protein detection assay.
The ability to identify ultra rare proteins in blood could save hundreds of thousands of lives in certain cases, for instance, the diagnosis of serious brain injury or the early detection of specific cancers, which contain very small quantities of relevant biomarkers.
Existing ultrasensitive protein detection techniques rely on costly optics, fluid handlers, and bulky instruments, which limits their use to lab settings. These techniques usually involve serially generating, controlling and measuring tens of millions of droplets, and this whole process takes several days.
Now, researchers at the University of Pennsylvania have built a new method that can identify single proteins within a few minutes, using off-the-shelf components.
They used a group of strobing LED lights, a conventional mobile camera, and microfluidic droplet generators to build a system that is 1000x more sensitive and significantly less expensive than the existing state-of-the-art protein detection assay.
Standard Protein Detection Assay Vs New Technique
The standard protein assay named enzyme-linked immunosorbent assay (ELISA) was first described in the late 1970s. In this analytical biochemistry assay, antibodies are attached to the proteins in question and then changes in the sample’s color (in response to enzymes attached to the antibodies) are analyzed.
It can be performed through numerous point-of-care diagnostic tools, such as home HIV tests. However, the method doesn’t work if the concentration of proteins is very low.
The newly developed method, on the other hand, can precisely count those proteins, with nearly a thousand times more sensitivity. It measures a single protein at a time, by splitting the sample into microdroplets, each containing either one protein or none at all.
To speed up the process, researchers have devised hundreds of microdroplet generators that can work in parallel. A conventional cellphone camera is used to identify whether a microdroplet consists of a fluorescent-marker-bound protein or not.
New detecting system using a cellphone camera to capture microdroplets | Courtesy of researchers
But since, a cellphone camera can only capture about 100 images per second (which is too slow for this process), the signals from two consecutive droplets would overlap.
To solve this issue, they used a light source to illuminate the droplet 1000x faster than the camera’s framerate. They encoded the strobing light with a signal to isolate one microdroplet from others. The patterns of strobed light never repeat itself, thus each signal gets imprinted with a unique barcode.
Three Key Innovations
The new method is based on the following three key innovations:
- Hundreds of droplet generators etched into a single chip so that they all can work in parallel.
- Mobile phone imaging to speed up the fluorescence detection of droplets.
- Integration of on-chip delay lines and sample processing to enable serum-to-answer device operation.
This ultrasensitive, multiplexed biomarker detection technique can be brought directly to the point of use, where digital assays can have a major impact.