Abstract
Highly sensitive, label-free detection methods have important applications in fundamental research and healthcare diagnostics. To date, the detection of single nanoparticles has remained largely dependent on extremely precise spectral measurement, which relies on high-cost equipment. Here, we demonstrate a simple but very nontrivial mechanism for the label-free sizing of nanoparticles using the far-field emission of a photonic molecule (PM) around an exceptional point (EP). By attaching a nanoparticle to a PM around an EP, the main resonant behaviors are strongly disturbed. In addition to typical mode splitting, we find that the far-field pattern of the PM is significantly changed. Taking a heteronuclear diatomic PM as an example, we demonstrate that a single nanoparticle, whose radius is as small as 1 nm to 7 nm, can be simply monitored through the variation of the far-field pattern. Compared with conventional methods, our approach is much easier and does not rely on high-cost equipment. In addition, this research will illuminate new advances in single nanoparticle detection.
Highlights
The early-stage detection and characterization of single pathogens and viruses are of central importance for disease diagnosis, disease control, environmental monitoring, emergency response, and homeland security[1]
Our findings are based on the recent developments on exceptional point (EP)
We have demonstrated that the far-field pattern is highly sensitive to the target nanoparticle
Summary
The early-stage detection and characterization of single pathogens and viruses are of central importance for disease diagnosis, disease control, environmental monitoring, emergency response, and homeland security[1]. The first one was pioneered by Vollmer and Arnold in 200219, where the bound molecules can be monitored through the shift of resonant wavelengths in a microsphere This method has quickly attracted considerable research attention and has been successfully utilized to detect single viruses and single molecules[20,21,22,23]. In 2009, Zhu et al demonstrated a different mechanism to detect nanoparticles by measuring mode splitting in an ultrahigh Q microtoroid[24,25,26,27] This new finding can monitor the size of nanoparticles, but it can better suppresses the noise that the first method suffers from[24]. Taking the WGM cavity as an example, Wiersig applied this concept to label-free detection and demonstrated a threefold enhancement in sensitivity, which is extremely important for the improvement of the detection limit[31]. We explore the possibility of single nanoparticle detection through the variation of far-field emissions
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