Exceptional Points Detection for Biosensing
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Detection of target signals is commonly performed using sensors whose working principle relies on probing degenerate energy levels, namely, resonant frequencies. The sensor response is typically linear and proportional to signal perturbations, but, in many cases, the target signals are found to be weak. In these lines, exceptional point (EP)-based sensors show their true value, as their development is engineered around their peculiar property of significantly enhanced sensitivity. EPs are degeneracies that exist only in non-Hermitian systems and occur when not only the eigenvalues degenerate, but the associated eigenvectors also collapse. When non-Hermitian sensors operate near an EP, a small external perturbation can strongly lift the modal degeneracy. This results in a spectral splitting that can be quantitatively measured. For a system operating at an EP of order n, the eigenvalue splitting typically scales with the nth root of the perturbation strength, thereby offering enhanced sensitivity to extremely small perturbations. This enhanced sensing capability enables applications that range from consumer electronics and industrial systems to healthcare, environmental monitoring, and structural health monitoring (SHM). In this study, we exploit this concept to develop biosensors capable of detecting subtle variations of cells, such as density, viscosity, compressibility, etc. In particular, the proposed sensing scheme is used for measuring mechanical biomarkers of individual cells in high throughput for both fundamental studies and clinical applications.
