Incoherent broadband cavity-enhanced absorption spectroscopy for sensitive measurement of nutrients and microalgae

Incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS) can achieve sensitive measurements at trace concentrations for liquid phase marine samples. The IBBCEAS system consists of a cavity-enhancement module (CEM) and a transmission hyperspectral module (THM). The CEM has cavity-enhancement factors up to 78 at 550 nm. Measurements were obtained over a wide wavelength range (420–640 nm) with a halogen lamp, and the optical cavity was formed by two concave highly reflective mirrors (${\rm{R}} = {0.99}$). The minimum detectable absorption coefficient ${\alpha _{{\min}}}$ of ${7.3} \times {{1}}{{{0}}^{- 7}}\;{\rm{c}}{{\rm{m}}^{- 1}}$ at 550 nm corresponds to a limit of detection for nutrients of 780 pM. The spectral resolution of the THM is 3 nm in the wavelength range of 400 to 750 nm. We performed the IBBCEAS measurements for biological and chemical substances, including nutrients, microalgae, and Cy5 dye. The concentrations of nutrients in a deionized water environment and artificial seawater environment were measured at nanomolar levels; the concentration of microalgae phaeocystis was detected with ${3.46} \times {{1}}{{{0}}^4}/{\rm{mL}}$, and fluorescence substances such as Cy5 dye could be measured at 0.03 mg/L. Experimental results show that the IBBCEAS system has the capability for sensitive measurements of biological and chemical substances and has strong potential for in situ ecological marine environmental monitoring function.