The Golden Bullet

Gold and cell membranes have become a micro robot to fight bacteria

Grigory Kopiev, N+1

American researchers have created a medical micro robot from a golden particle covered with a hybrid membrane, which, in turn, is made of erythrocyte and platelet membranes. The robot is able to capture dangerous bacteria and toxins produced by them, and its movement in the body can be controlled using ultrasound, the authors say in the journal Science Robotics (Hybrid biomembrane–functionalized nanorobots for simultaneous removal of pathogenic bacteria and toxins).

Scientists are developing not only large robots, but also microscopic ones designed, among other things, to work inside the human body. They can solve different tasks — for example, perform targeted drug delivery or capture individual cells. Since it is very difficult to create artificial engines and sensors for such small robots, developers often equip them with elements from living organisms. For example, last year, German researchers turned a sperm cell into a hybrid drug deliverer to a cancerous tumor.

A group of scientists from the University of California, San Diego, led by Joseph Wang, used a similar approach and created a micro robot using natural cell membranes to capture bacteria and toxins. The authors decided to target the robot to gram-positive bacteria, in particular, Staphylococcus aureus. These bacteria secrete pore-forming toxins that create holes in cell membranes that can lead to lysis.

Robot operation diagram (drawings from an article in Science Robotics)

The researchers were able to create a robot that captures both the bacteria themselves and the toxins they emit. Since gram-positive bacteria in the body often bind to platelets, and pore-forming toxins with red blood cells, scientists decided to combine their properties by creating a hybrid membrane. They took a solution with erythrocytes and platelets, and mixed it with ultrasound, creating single vesicles from two types of membranes. After this solution was mixed with elongated gold particles about two micrometers long, the membranes spontaneously fixed around the particles.

Staphylococcus aureus captured by a robot

You can control the robot's movement using ultrasound — it moves in the opposite direction from the emitter. The authors showed the effectiveness of moving robots by comparing them with static ones. Scientists placed robots in environments containing a strain of Staphylococcus aureus and one of the groups was moved by ultrasound. Then they compared the number of bacteria caught using a fluorescent marker and saw that in the group of moving particles the intensity of the glow was 3.5 times higher. In addition, the researchers tested the effect of robots on bacterial toxins and found that the presence of such robots in a solution with erythrocytes leads to a noticeably lower level of hemolysis — by 5.5 percent.

Recently, German scientists have created another robot based on living cells. They attached an E. coli bacterium with flagella to a red blood cell containing the drug, as well as superparamagnetic particles. As a result, the authors created a design in which the bacterium is responsible for moving forward, and the erythrocyte corrects the direction under the influence of an external magnetic field.

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