Many studies in biology and medicine rely on detecting protein concentrations in samples. Disease diagnoses, treatment methods, and proteomic studies often depend on detecting minute protein concentrations and are therefore limited by the protein detection limit of the sensor used. Faced with this limit, researchers are forced to employ more expensive detectors or perform more complicated assays.

Fan et al. describe a method of concentrating proteins in a sample using an inexpensive isoelectric focusing technique, which is capable of detecting proteins at concentrations four times lower than the device detection limit.

The device consists of two concentric rings overlaid on the desired sample, with a voltage applied between them. This voltage produces a current, and therefore a pH gradient, across the rings that pulls proteins to its center.

“Since we can control the pH within that range, the proteins can be concentrated through a technique called isoelectric focusing,” said author Jinglei Ping. “Proteins will take on a charge and move to the electrode with the opposite polarity until they are charge neutral. The central region is where those proteins stop moving and become concentrated.”

In tests, the device demonstrated not only an ability to concentrate proteins, but also an ability to lower their random motion, resulting in less measurement noise.

The authors are looking forward to testing the capabilities of this technique in their own research.

“We are going to integrate this technique with cell systems, such as cancer cells, to see how we can use it to deliver proteins,” said Ping. “We are also interested in integrating this technique into a lab chip device for detection of proteins with higher sensitivity.”

Source: “On-chip microscale isoelectric focusing enhances protein detection limit,” by Xiao Fan, Xiaoyu Zhang, Huilu Bao, Xin Zhang, and Jinglei Ping, Applied Physics Letters (2024). The article can be accessed at https://doi.org/10.1063/5.0190380.