Optical Detection of Blood in Cerebrospinal Fluid Using a Laser and Position-Sensitive Detector

Abstract

The detection of blood in cerebrospinal fluid (CSF) is a critical diagnostic indicator forlife-threatening conditions such as hemorrhagic stroke and traumatic brain injury. Current detection methods rely on invasive sampling which can delay diagnosis and treatment in emergency settings. This report presents a laser-based optical system for detecting the presence of hemoglobin in fluid samples. The system measures transmitted laser intensity through a fluid-filled channel using a position-sensitive detector (PSD) and red laser, with changes in intensity correlating to hemoglobin concentration. Initial trials using blue food coloring confirmed the theoretical relationship between concentration and light absorption, validating the experimental setup. Hemoglobin testing was then conducted using a 9 mL fluid channel with a measured optical path length of 12 mm, achieving reliable detection between 1.88 µM and 126.85 µM. However, the system exhibited a strong linear relationship only up to approximately 60 µM. Concentrations greater than this had greater laser absorbance leading to more noise in the natrual logarithm values, and in the highest concentration there was total absorbance of the red laser. To overcome this, a smaller 1.25 mL fluid channel with a 5 mm path length was introduced, allowing detection up to 155.04 µM, with the relationship between concentration and the natural logarithm of the intensity being linear throughout. These findings align with the Beer–Lambert Law, which predicts reduced absorbance for shorter path lengths at the same concentration. Statistical validation with distilled water trials showed high repeatability, with a coefficient of variation of only 0.07%, confirming the PSD’s stability and sensitivity. The results demonstrate that optical hemoglobin detection is feasible within clinically relevant concentration ranges. Future work may explore alternate wavelengths, cantilever optimization for flow tracking, and system integration into a compact diagnostic tool for medical professionals.