PolyU researchers pioneer 3D micro-printed sensors to advance on-chip biosensing for early disease detection

Early-stage disease diagnosis relies on the highly sensitive detection of biomarkers. Optical whispering-gallery-mode (WGM) microcavity sensors have emerged as a highly promising technology for precise, label-free biosensing. However, major challenges remain in the rapid fabrication of large-scale arrayed WGM microcavity sensors and their integration into lab-on-a-chip devices for biomedical applications. In a noteworthy advance, researchers at The Hong Kong Polytechnic University (PolyU) have developed a novel 3D micro-printed WGM microlaser sensor for highly sensitive on-chip biosensing. This innovation drives the development of next-generation biosensing tools, enabling direct, ultrasensitive and quantitative measurement of biomarkers for early disease detection.

Prof. ZHANG -ping, Professor of the Department of Electrical and Electronic Engineering at PolyU, and his research team have invented the new sensor—a 3D micro-printed Limacon-shaped WGM microlaser sensor—by combining flexible 3D micro-printing technology with the optical advantages of WGM microlasers. This innovation achieves both easier light coupling and superior biosensing performance, paving the way for impactful on-chip biosensing applications.

Prof. Zhang said, “In the future, these WGM microlaser sensors could be integrated into a microfluidic chip to enable a new generation of lab-on-a-chip devices for ultrasensitive, quantitative detection of multiple biomarkers. This technology could be used for the early diagnosis of diseases such as cancers and Alzheimer's disease, or for fighting major health crises such as the COVID-19 pandemic.”

The newly developed microlaser sensor design overcomes many challenges that have hindered the integration of such sensors into lab-on-a-chip systems for point-of-care medical diagnostics. The research further reveals that the microlaser sensor’s resonant nature and its very narrow linewidth of lasing peaks enable the detection of extremely small concentrations of human immunoglobulin G (IgG), a common antibody found in blood and other body fluids.

Experimental results showed that the sensor can detect human IgG at a detection limit of approximately 70 ag/mL, highlighting its potential for ultralow-limit detection of biomarkers in early disease diagnosis. The research, “3D micro-printed polymer Limacon-shaped whispering-gallery-mode microlaser sensors for label-free biodetection,” has been published in Optics Letters, and highlighted with a news release by international optical society OPTICA.

The state-of-art facilities at PolyU have played a crucial role in supporting the researchers’ groundbreaking innovations. Prof. Zhang remarked, “This innovative microlaser sensor was made possible by our in-house 3D micro-printing technology, which allowed for the rapid fabrication of the specially designed 3D WGM microcavity and high-precision trimming of its suspended microdisk.”

Integrating photonic sensors onto a chip is critical for advancing high-performance biosensing technology. Optical WGM microlaser sensors operate by circulating light resonantly within tiny microcavities. When target molecules bind to the cavity’s surface, they induce slight changes in the laser’s wavelength, enabling highly sensitive detection of biological substances.

However, one challenge in applying these sensors in real-life is the need to couple light entering and leaving them, which typically requires a tapered optical fibre with a diameter smaller than 2 microns. Such tiny fibres are not only difficult to align but also susceptible to various environmental disturbances. This limitation has hindered the integration of microlaser sensors into lab-on-a-chip devices for real-time, high-sensitivity detection of biomolecules.

Using the light emitted directly from the microlaser sensor offers a promising alternative to using tapered optical fibres for light coupling. However, the circular microcavities of conventional WGM microlasers make efficient far-field light collection difficult, thereby limiting the readability of the sensor’s weak signal.

To overcome this challenge, the research team designed a 3D WGM microlaser sensor featuring a Limacon-shaped suspended microdisk. This innovative design provides the sensor with both low lasing threshold and directional light emission, improving light coupling efficiency for practical on-chip integration.

Leveraging their self-developed 3D micro-printing technology, which offers high resolution and flexibility, the team successfully fabricated the arrays of WGM microlaser biosensors at a remarkable speed. Experimental results showed that the microlaser biosensors exhibited a very low lasing threshold of 3.87 μJ/mm² and a narrow lasing linewidth of about 30 pm. Notably, the sensors were capable of detecting IgG at a concentration as low as attograms per millilitre, highlighting their potential for ultrasensitive biomarkers detection in early disease diagnosis.

Moving forward, Prof. Zhang plans to integrate the microlaser sensors into a microfluidic chip to develop optofluidic biochips for rapid, quantitative and simultaneous detection of multiple disease biomarkers.

*Notes: A lab-on-a-chip is a device that integrates one or several laboratory functions (e.g. chemical or biological analysis) on a single integrated circuit (commonly called a “chip”) of only millimetres to a few square centimetres to achieve automation and high-throughput screening.

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