A reusable sensor built with tiny gold particles and a common sugar can identify a wide range of concentrations of the bacterium Escherichia coli at low cost, which could potentially protect millions of people from bacteria in food or sewage water.
The self-powered nanosensor, described in a study published in Nano Energy on March 22, uses electric energy to identify a common strain of E. coli. Corresponding author Zong-Hong Lin told The Academic Times that his research group is "interested in bacterial detection for health care and food safety reasons as well as environmental issues." One major application is in foodborne illnesses.
Food recalls have been increasingly common in the past few years, with pathogenic E. coli recently identified in romaine lettuce and ground beef. The Centers for Disease Control and Prevention reports that almost 10 million Americans are affected by these outbreaks every year — that's almost one in every 30 people in the U.S. Eating food contaminated by E. coli can lead to diarrhea and other stomach issues.
The bacteria affects a wide range of organs, as E. coli can lead to urinary tract infections (UTIs) when it travels from the intestines, where it helps the body digest food as part of gut microflora, to the urethra. Every year, over 150 million people visit hospitals across the world to be treated for UTIs. Up to 95% of these infections in women are caused by E. coli, and the strain chosen for this study is the most common source of them. The ability to diagnose and treat UTIs is also important for male patients with prostate cancer, who often suffer from recurrent infections caused by E. coli. Lin, who is also an associate professor at National Tsing Hua University, saw a need for efficient and cheap technology to detect this bacteria.
Lin and his team developed a new type of biosensor to identify E. coli in a sample. The sensor measures electric outputs from the interaction of a solid and a liquid layer inside the device. When the solid and liquid substances come into contact, electricity is transferred between them in a triboelectric charge. The process is very similar to how static electricity is created when a person rubs a balloon on their hair. Though the charges occur on a nanolevel, they are easily measured using a triboelectric nanosensor.
The team's triboelectric nanosensor looks at the interaction of carbohydrates and proteins in order to detect E. coli. The solid layer inside the sensor is made from gold nanoparticles coated in D-mannose, a type of sugar found in cranberries, peaches and many other fruits. When covered in sugary carbohydrates, the gold nanoparticles act as a probe to detect bacteria, as they bind to proteins in the strain tested in this study, E. coli ORN178. The sensor's liquid layer is a phosphate buffer saline, which carries an electrical charge. If bacteria is in the sample, the device produces more electricity as the solid gold layer is less able to transfer energy to the liquid buffer. This increase in the nanosensor's voltage marks the presence of E. coli.
Not only is the team's technique cheaper than any currently on the market, but it is also reusable. "Most of the commercially available bacterial-detection assays" are only single use, Lin explained. "After that, the sensor cannot be used for a second time, and it must be disposed of, which poses different biohazards," he continued. The sensor can also function without an external power supply, allowing the device to be used in other kinds of technology.
In future studies, Lin said that the "nanosensor can be employed to detect different biomolecules and pathogens and open a new window to detect different protein biomarkers." The technique's focus on proteins could even help doctors diagnose cancer at very early stages. Medical researchers examine the interactions between antigens and antibodies that signify the presence of cancer cells, and this process could be carried out in the nanosensor.
The group thinks that many companies could adopt this new technology in the future. Environmental firms could design a portable device for in-field detection of bacteria, they reported in the study. According to Lin, those in the food industry could "install the triboelectric nanosensor on the fingertip of a robotic hand, which can directly monitor the pathogenic infection by just touching the infectious food." A hands-free way to test pathogens means that both workers and consumers could avoid biohazards. Lin also sees potential for "wireless environmental and health monitoring using a smartphone or laptop" with a transmission module.
The team is currently developing other self-powered sensors, as Lin thinks the power source "has always been the bottleneck to overcome" in wearable electronics. Some harvest "energy from human motions or thermal energy in the environment to directly power wearable systems," Lin said. He thinks these textiles and lightweight nanogenerators could be fused with "next-generation smart clothes" — an innovative concept in which electronics are powered with the kinetic energy of a heartbeat or a breath.
The study, "Carbohydrate-protein interactions studied by solid-liquid contact electrification and its use for label-free bacterial detection," published March 22 in Nano Energy, was authored by Yu-Ping Pao, Yu-Zih Lin, Subhodeep Chatterjee, Subhajit Saha, and Naveen Tiwari, National Tsing Hua University; Ching-Ching Yu and Yu-Ting Huang, National Chung Cheng University; Chih-Cheng Wu, National Tsing Hua University, National Taiwan University, National Taiwan University Hospital, and National Health Research Institutes; Dukhyun Choi, Kyung Hee University; and Zong-Hong Lin, National Tsing Hua University and Kyung Hee University.