Liquid crystal biosensing platform based on whispering gallery mode laser for Aβ42 detection

Alzheimer's disease (AD) is an irreversible and progressively worsening neurodegenerative disorder. Amyloid beta (Aβ42) plays a crucial role in the early diagnosis of this disease. However, the concentration of Aβ42 in the blood is extremely low, which poses a challenge for Aβ42 detection. Herein, a liquid crystal (LC) biosensing platform based on whispering gallery mode (WGM) laser was developed for rapid and real-time monitoring of the AD-related biomarker Aβ42. The LC microcavities were functionally modified using cetyltrimethyl ammonium bromide (CTAB) and RNA aptamers. Based on this, the quantitative monitoring mechanism of Aβ42 was analyzed, stemming from the interaction between the negatively charged RNA aptamer and CTAB, leading to the reorientation of LC molecules. This alters the refractive index distribution within the microcavity, thereby enabling the shift of the WGM spectrum. The dynamic changes of molecular orientation in the LC microcavity were monitored by polarization optical microscopy and spectral analysis. The experimental results showed that the total shifts in the resonance spectrum were directly proportional to the concentration of Aβ42 within the range of 0-1000 pg/mL. The sensitivity of the sensor is 0.003 nm/pg/mL. The experiment further confirmed the practicability of this sensor in the mouse serum. The sensor is inexpensive, easy to manufacture and fast and it is potentially useful for AD-related biomarker screening after further validation.