An international research team led by Prof. YANG Hui Yang from Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences and Prof. WANG Zengbo from Bangor University, UK has developed a near-field optical sensing platform capable of generating arrayed light beams with high intensity and high spatial constraint in semi-open areas.  

The sensing platform is based on an array of dielectric microsphere lenses with laser-machined semi-open microwell on top of each microsphere (μ-well lens). The result showed that it can be used in biosensors to detect and quantify bio-chemical analyte of ultra-low concentration, which is a first for a biosensor of this kind. 

The study was published in Sensors and Actuators B: Chemical on Jan. 19, 2022. 

Dielectric microsphere lenses can squeeze light into the subwavelength scale via photonic nanojet (PNJ) focusing. The light is confined and concentrated into a very small area, resulting in a light field that is orders of magnitude higher than the incident light. Therefore, bio-chemical analytes (molecules, ions, and proteins, etc.) in the focus zone of the PNJ experience an enhanced electromagnetic excitation which stimulates strong light–matter interactions. Consequently, it generates profound effect on the efficacy of various optical processes, such as field emission enhancement, radiation pattern modulation, and scattering signal increase. This has brought the PNJ based optical convergence approach as a promising technology in the field of near-field optical sensing.  

However, there are two major challenges exist in the realization of this near-field optical sensing technology: 

1. The PNJ with relatively small effective volume is, in general, generated in a free space perpendicular to the substrate containing dielectric microspheres. Thus, introducing the objects of interest into this volume is rather difficult. 

2. Due to the heterogeneous distribution of the PNJ intensity field, signals that report the strength of light–matter interactions between the objects and the PNJ could exhibit server fluctuations when spatial location of the object varies. 

"For the first time in this field, we have proposed a near-field optical sensing platform based on localized photonic nanojets (L-PNJs), which solved the above two challenges and achieved efficient signal amplification and quantitative biosensing," said Prof. WANG.  

The team utilized a nanosecond laser to precisely machine micron-scale semi-open microwells on the top of each dielectric microsphere lens. The resulted μ-well lens can not only generate a strong L-PNJ, but also can precisely and passively trap a single micron-scale analytes into the L-PNJ. Therefore, this novel design greatly improves the efficiency of introducing targets into the L-PNJ and suppresses their signal fluctuations.  

Moving forward, they have employed this μ-well lens for bead-based biomolecule concentration analysis, achieving high-sensitivity detection and greatly improving the detection limit.  

"This sensing platform is promising for development of next-generation on-chip signal amplification and quantitative detection systems as well as for investigating a wide range of light–matter interaction processes," said Prof. YANG. 

Media Contact:
ZHANG Xiaomin
Email:xm.zhang@siat.ac.cn