A compact multi-channel fluorescence sensor with ambient light suppression

Abstract

A multi-channel fluorescence sensor has been developed for process monitoring and fluorescence diagnostics. It comprises a fiber-optic set-up with an immersion probe and an intensity-modulated high power ultraviolet light-emitting diode as a light source for fluorescence excitation. By applying an electronic lock-in procedure, fluorescence signals are selectively detectable at ambient light levels of 1000 000 times higher intensity. The sensor was designed to be compact, low cost and easily adaptable to a wide field of application. The set-up was used to simultaneously monitor three important metabolic fluorophores: NAD(P)H, flavins and porphyrins during the cultivation of a baker's yeast. Moreover, the accumulation and degradation kinetics of protoporphyrin IX induced by 5-aminolevulinic acid on the skin could be recorded by the sensor. The detection limit for protoporphyrin IX was determined to be 4 × 10−11 mol L−1. The linear signal amplification of the sensor and time courses of fluorescence signals monitored during yeast fermentations were validated using a commercial CCD spectrometer. The robust and flexible set-up of the fiber-optic measurement system promises easy implementation of this non-invasive analytical tool to fluorescence monitoring and diagnostics in R&D and production.

NADH-fluorescence scattering correction for absolute concentration determination in a liquid tissue phantom using a novel multispectral magnetic-resonance-imaging-compatible needle probe

“…Equation (1) represents the best fit to the measured values. At very low fluorophore (NADH) concentrations, the values follow an approximately linear trend [38,39]. In this system, scattering and absorption were noticeable at concentrations greater than 0.2 mmol l −1 and reduced the penetration depth of the light and, consequently, the measurement volume of the used optical probe.…”

Macroscale fluorescence imaging against autofluorescence under ambient light

“…In addition, macroscale fluorescence imaging can suffer from ambient light (up to sunlight in the case of outdoor observations); thus, its application is typically restricted to light-tight enclosures or darkrooms. In macroscale fluorescence imaging, the utilization of modulated illumination and image acquisition in homodyne detection 4 , 5 and pulsed excitation and time-gated detection 6 , 7 has been already proposed for retrieving fluorescence signals against ambient light. In contrast, there remains a demand for reliable strategies for eliminating the detrimental effects of autofluorescence in this imaging modality.…”

Dynamic Contrast for Plant Phenotyping

“…However, subtraction suffers from a temporally varying lighting environment and it cannot be used if ambient light is too strong as a consequence of the shot noise. Pulsed excitation light of μs–ms duration associated with gated detection has provided a second approach for fluorescence imaging under room light to sunlight conditions. ,− Eventually, lock-in imaging has been implemented to distinguish a fluorescence signal from ambient light by retrieving the background-free modulated component of fluorescence under periodic modulation of excitation light. , In contrast to the two preceding approaches, it benefits from a higher signal-to-noise ratio (SNR) due to frequency-domain noise filtering. In addition, it is insensitive to irregular fluctuation of ambient light.…”