Antibody tests are often used to determine whether individuals have been exposed to certain bacteria or viruses. For most existing antibody tests, the process goes something like this: A vial of blood is drawn from the individual, the vial is sent to a lab, then a trained technicians performs the antibody test and sends back the results. The current process is less than ideal for a few reasons. For one, blood draws are invasive and can be painful. Also, getting results could take days, due to the time required to deliver and process the sample. Lastly, costs can be high, since the need for trained professionals and specialized instruments in laboratory settings adds to the cost of each test.
What if all you needed to do for an antibody test was apply a single drop of blood onto a thin piece of film, and you would get results on the spot within five minutes? Scientists have recently developed an antibody test based on bioluminescent technology that could make this a reality. They describe their findings in a recent study published in ACS Sensors.
The new antibody test uses a bioluminescent sensor called Luminescent Antibody Sensing Protein (LUMAB) that contains a blue light-emitting luciferase (NanoLuc® luciferase) and a green fluorescent protein (mNG). In the absence of targeted antibody, the NanoLuc® luciferase and mNG are in proximity, resulting in efficient bioluminescence resonance energy transfer (BRET). The result is the emission of green light. In the presence of antibody, the antibody binds to specific sequences within the sensor and separates the NanoLuc® and mNG proteins, which results in a color shift from green to blue. The bluer the glow, the higher the concentration of antibody in the blood sample.
In order for this biosensor to work, luciferin must be added to catalyze the luciferase reaction, and it is crucial that luciferin does not mix with luciferase before reacting with the blood sample. Previous studies have solved this problem by using two dried layers of paper, one soaked with luciferin and the other with the LUMAB. As long as the paper is dry, the chemicals will not mix. However, when blood is added to these two layers stacked atop one another, the liquid soaks through, allowing the chemicals in both layers to mix and react. The problem with this approach is that it requires a large volume of blood. The authors wanted to develop a new method that could use just a single drop, which would simplify sample collection from a blood draw to a finger prick. With this in mind, they came up with an ingenious alternative to paper: cotton thread.
The new microfluidic thread-based analytical device (µTAD) consists of two intertwisted cotton threads—one soaked with luciferin, the other with LUMAB. The use of thread instead of paper not only reduces the volume of blood needed and speeds up the reaction time, but also allows the arrangement of several different LUMAB threads on a single device. For example, different LUMAB threads sewn in a starburst pattern can detect multiple antibodies from one sample of blood dropped in the center of the star. With this approach, the authors were able to detect the presence of three different antibodies (indicating exposure to the flu, dengue fever and HIV) on one device using the same drop of blood.
The next challenge was to figure out how to detect the blue-green light without using laboratory equipment. As it turns out, the blue-green glow can easily be captured in a dark room using a regular smartphone camera. The human eye cannot easily distinguish the ratio of blue to green light, but an app on the phone can, and this color ratio is used to estimate how much antibody is present. But what if the clinic does not have access to a dark room? The authors developed a 3D-printed customized lens adaptor, roughly the size of an ice cube, that blocks light and fits snugly on any smartphone.
This µTAD device is still in the early stage of development, and more research is needed to ensure testing accuracy. However, this study shows the potential of using bioluminescent sensor proteins to develop faster and user-friendly antibody tests. These types of testing devices are especially helpful for remote clinics that do not have easy access to sophisticated testing labs, and there is hope that they could improve the health of those most in need.
Learn more about the many applications of the NanoLuc® Luciferase!
References
Tomimuro K. et al. Thread-Based Bioluminescent Sensor for Detecting Multiple Antibodies in a Single Drop of Whole Blood. (2020) ACS Sensors. 5(6), 1786—1794
Perkins S. A glowing new way to measure antibodies. Science News for Students
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