The growing presence of nanoplastics in the environment has highlighted the need for simpler detection methods, leading researchers at Science Tokyo to develop a rapid biosensor for detecting polystyrene nanoparticles in water. Tested in both model water samples and real water samples spiked with polystyrene nanoparticles, the device detected 50 nm particles within 20 minutes without labeling or extensive sample preparation. The technology could support efforts to understand and address nanoplastic accumulation in the environment.
Plastics fragment into increasingly smaller particles over time, eventually forming nanoplastics, particles ranging from 1 to 1,000 nm in size. These nano-sized plastic particles have permeated the environment and have been detected in living organisms, including the human body, raising growing concerns about their potential impacts on the environment and human health. The current analytical techniques used to detect nanoplastics include microscopy and spectroscopy methods. However, these conventional approaches require expensive equipment and extensive sample preparation, limiting their practicality for routine monitoring.
A research team at Institute of Science Tokyo (Science Tokyo), Japan, has now developed a biosensor that can rapidly detect polystyrene nanoparticles (PS-NPs) in fresh water. PS is one of the most commonly used plastic materials in both household and industrial applications, making PS-NPs an important target for nanoplastic detection. By enabling selective, label-free detection in aqueous environments with minimal sample preparation, the device could significantly improve water quality assessment, marking an important step toward practical nanoplastic detection.
The study was led by Associate Professor Mana Toma of the Department of Electrical and Electronic Engineering, School of Engineering, in collaboration with Assistant Professor Shuo Cheng from the School of Environment and Society, Japan
The paper was made available online on May 9, 2026, and will be published in Volume 308 of the journal Biosensors and Bioelectronics on September 15, 2026.
"The extremely small size of nanoplastics makes them difficult to detect using conventional methods. We addressed the challenge by designing a biosensing platform that selectively captures PS-NP particles at the sensor surface and detects them optically," says Toma.
A biosensor consists of biorecognition elements that can bind with specific targets, producing a measurable signal. Here, a PS-binding peptide serves as the recognition element. The peptide was immobilized onto a thin gold film through a polyethylene glycol (PEG) linker, which minimizes non-specific binding and enhances the selective capture of PS-NPs.
The biosensor works using surface plasmon resonance (SPR), an optical sensing technique that detects tiny refractive index changes at a surface in real time. In this setup, laser light is directed through a high refractive index glass prism onto a thin gold film, exciting surface plasmons, which are collective oscillations of free electrons at the metal surface. When PS-NPs bind to the sensor, they change the local refractive index near the gold film, shifting the resonance angle. In the present system, this binding-induced SPR shift is monitored as a change in reflected light intensity at a selected incident angle. By comparing this intensity changes with a calibrated SPR response versus concentration curve, the system quantifies PS-NP concentrations in water.
The researchers tested the biosensor in laboratory water designed to mimic the ionic composition of freshwater, to which they added PS-NPs at known and controllable concentrations. In these samples, the proposed biosensor was able to detect 50 nm PS-NPs within 20 minutes and achieved a detection limit as low as 1.3 μg/mL. They also validated the detection in environmentally relevant samples using aquarium water and pond water spiked with PS-NPs.
"By simplifying the detection process, this biosensor could make nanoplastic monitoring more accessible than conventional methods that require specialized instruments and extensive sample preparation," says Toma.
The continued use and degradation of plastics will inevitably increase nanoplastic accumulation in the environment. By simplifying detection and making monitoring more practical, the proposed biosensor could help researchers better understand how nanoplastics spread and behave, supporting efforts to address this growing environmental challenge.
