The present work demonstrates the integration of hollow core photonic crystal fibers (HC-PCF), microfluidics, and statistical analysis for monitoring biomolecules using Raman spectroscopy. HC-PCF as a signal enhancer has been proven by many researchers. However, there have been challenges in using HC-PCF for practical applications due to limitations such as coupling, stability, evaporation, clogging, consistent filling, and reusing the same fiber. This limited the potential of HC-PCF to detect low concentrations of liquid samples, which is why HC-PCF still hasn’t transcended the lab barriers. The current device is based on an H-design lay-out which uses the pressure difference between the two ends of the fiber for filling and flushing the liquid samples. This mitigated several issues related to device performance by allowing us to fill the fiber with liquid samples consistently, rapidly and reproducibly. The resulting Raman signals were significantly more stable as various concentrations of ethanol in water were sequentially introduced into the fiber. The scheme also allowed us to overcome the barrier of predicting low concentrations by applying Partial Least Square (PLS) technique which was done for the first time using HC-PCF. Thus, the present scheme paves path for the inclusion of HC-PCF in the main stream point-of-care technology.
Heparin is the most widely used anti-coagulant for the prevention of blood clots in patients undergoing certain types of surgeries including open heart surgeries and dialysis. The precise monitoring of heparin amount in patients’ blood is crucial for reducing the morbidity and mortality in surgical environments. Based upon these considerations, we have used Raman spectroscopy in conjunction with partial least squares (PLS) analysis to measure heparin concentration at clinical level which is less than 10 United States Pharmacopeia (USP) in serum. The PLS calibration model was constructed from the Raman spectra of different concentrations of heparin in serum. It showed a high coefficient of determination (R 2 >0.91 ) between the spectral data and heparin level in serum along with a low root mean square error of prediction ∼4 USP/ml . It enabled the detection of extremely low concentrations of heparin in serum (∼8 USP/ml ) as desirable in clinical environment. The proposed optical method has the potential of being implemented as the point-of-care testing procedure during surgeries, where the interest is to rapidly monitor low concentrations of heparin in patient’s blood.
The present work explores the feasibility of using surface enhanced Raman scattering (SERS) for detecting the
neurotransmitters such as glutamate (GLU) and gamma-amino butyric acid (GABA). These amino acid neurotransmitters
that respectively mediate fast excitatory and inhibitory neurotransmission in the brain, are important for neuroendocrine
control, and upsets in their synthesis are also linked to epilepsy. Our SERS-based detection scheme enabled the detection
of low amounts of GLU (10<sup>-7</sup> M) and GABA (10<sup>-4</sup> M). It may complement existing techniques for characterizing such
kinds of neurotransmitters that include high-performance liquid chromatography (HPLC) or mass spectrography (MS).
This is mainly because SERS has other advantages such as ease of sample preparation, molecular specificity and
sensitivity, thus making it potentially applicable to characterization of experimental brain extracts or clinical diagnostic samples of cerebrospinal fluid and saliva. Using hollow core photonic crystal fiber (HC-PCF) further enhanced the
Raman signal relative to that in a standard cuvette providing sensitive detection of GLU and GABA in micro-litre
volume of aqueous solutions.