Altaf Khetani

Raman Spectroscopy of Nanoparticles Using Hollow-Core Photonic Crystal Fibers

Hollow-core photonic crystal fibers (HC-PCF) were employed for enhancing the Raman signal obtained from ZnO nanoparticles (NPs) in solution. By selectively filling the core of HC-PCF, substantial enhancement in the Raman signal was obtained. By employing this technique, four different stages in the synthesis ZnO NPs were studied with record low pump power levels. The concentration of ZnO NPs in the system was <1% by weight of the total mass. Yet, the different synthesis stages could be differentiated and identified through the Raman modes obtained. It was also demonstrated that the concentration of NPs in solution could be obtained with sensitivity in the millimolar range. This could be achieved by examining the amplitude ratios of the relevant Raman modes.

Hollow core photonic crystal fiber as a reusable Raman biosensor

We report that a single hollow core photonic crystal fiber (HC-PCF) can be used for repetitive characterization of multiple samples by Raman spectroscopy. This was achieved by integrating the HC-PCF to a differential pressure system that allowed effective filling, draining and re-filling of samples into a HC-PCF under identical optical conditions. Consequently, high-quality and reliable spectral data could be obtained which were suitable for multivariate analysis (partial least squares). With the present scheme, we were able to accurately predict different concentrations of heparin and adenosine in serum. Thus the detection scheme as presented here paves a path for the inclusion of HC-PCFs in point-of-care technologies and environmental monitoring where rapid sample characterization is of utmost importance.

Hollow core photonic crystal fiber for monitoring leukemia cells using surface enhanced Raman scattering (SERS).

The present paper demonstrates an antibody-free, robust, fast, and portable platform for detection of leukemia cells using Raman spectroscopy with a 785-nm laser diode coupled to a hollow core photonic crystal (HC-PCF) containing silver nanoparticles. Acute myeloid leukemia is one of the most common bone marrow cancers in children and youths. Clinical studies suggest that early diagnosis and remission evaluation of myoblasts in the bone marrow are pivotal for improving patient survival. However, the current protocols for leukemic cells detection involve the use of expensive antibodies and flow cytometers. Thus, we have developed a new technology for detection of leukemia cells up to 300 cells/ml using a compact fiber HC-PCF, which offers a novel alternative to existing clinical standards. Furthermore, we were also able to accurately distinguish live, apoptotic and necrotic leukemic cells.

A novel method of using hollow-core photonic crystal fiber as a Raman biosensor

A new method for using a non-selectively filled hollow-core photonic crystal fiber (HC-PCF) as a sensitive Raman spectroscopy platform suitable for biosensing applications is presented. A 1550 HC-PCF was completely filled with ethanol (core and cladding holes). Using a 785nm excitation laser, the Raman spectrum of ethanol in the fiber core was obtained and compared with the equivalent Raman spectrum of an ethanolfilled cuvette. Using a relatively short 9.5cm length of HC-PCF, a Raman signal enhancement factor of 40 over a bulk solution of ethanol was observed under the same excitation conditions. The small sample volume utilized and longer interaction length provides the potential for compact, sensitive, and low-power Raman sensing of biological materials

Optimum Size and Volume of Nanoparticles Within Hollow Core Photonic Crystal Fiber

We investigate the effect of volume and size of silver nanoparticles (AgNP) on surface enhanced Raman scattering (SERS) signal of rhodamine 6G (R6G) within hollow core photonic crystal fiber (HC-PCF). The HC-PCF enhanced the Raman signal of R6G by a factor ~90 via photonic band gap. In addition, the optimal size and volume of AgNP enhanced the Raman signal of R6G by a factor of ~43, resulting in a total enhancement of ~4223 in HC-PCF. A comparison of AgNP enhancement factors in HC-PCF and bulk sample (cuvette) is presented at their optimal size and volume with respect to R6G. The SERS based HC-PCF sensing platform as optimized for R6G as a test molecule, was further utilized for monitoring adenosine for clinical application.

Study of surface enhanced Raman scattering (SERS) within hollow core photonic crystal fiber

The presented work aims to realize the surface enhanced Raman scattering (SERS) signal of rhodamine 6G (Rh 6G) molecule by non-selectively filling all the holes of hollow core photonic crystal fiber (HC-PCF) while exploiting the bandgap property of HC-PCF. As a consequence, strong mode field overlap with the analyte solution is achieved resulting in an amplified Raman signal with just a few milliwatts (∼2mW) of sample energy within the fiber core. The actual contribution of enhancement by HC-PCF has been deconvolved from that of nanoparticles in the overall Raman signal enhancement of Rh 6G. Finally, we report the enhancement factor of Raman signal of Rh 6G, filled within the different lengths of HC-PCF.

Laser flash photolysis with nanoliter samples: photonic crystal fibers as ultrasmall smart test tubes

Photonic crystal fibers play a dual function as a sample container as well as a photonic device supporting mode structure, and in doing so offer new opportunities for carrying out laser flash photolysis experiments with ultrasmall samples. Monitoring light can be transmitted in the fiber by total internal reflection or by the photonic bandgap guiding effect, depending upon the relative refractive index of the fiber material (usually silica) and the liquid filling the holes. Both offer opportunities for transient monitoring in time scales as short as tens of nanoseconds, with enhanced signals with respect to conventional (large sample) laser flash photolysis work.

Detection of amino acid neurotransmitters by surface enhanced Raman scattering and hollow core photonic crystal fiber

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 (10-7 M) and GABA (10-4 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.

Monitoring of adenosine within hollow core photonic crystal fiber by surface enhanced Raman scattering (SERS)

Hollow core photonic crystal fiber (HC-PCF) has emerged as a new generation micro-structured fibers with an ability to confine light within the core region. The possibility of infiltrating the analyte within the HC-PCF has further given boost to the strong light-matter interaction. It, therefore, lays a platform for harnessing the maximum potential of existing spectroscopic techniques in sensing broad range of molecules. The presented work aims to utilize one such technique known as surface enhanced Raman scattering (SERS) in conjugation with HC-PCF for monitoring adenosine in presence of nano structured materials. The novelty of the presented work primarily lies in realizing the SERS signal of adenosine molecule by non-selectively filling all the holes of HC-PCF while exploiting the bandgap property of HC-PCF. Such detection scheme facilitates enhancement in Raman signal by nano materials and HC-PCF. Additionally, an effort has been made to measure the actual contribution of enhancement by HC-PCF from that of nanoparticles in the overall Raman signal enhancement of adenosine.

Surface Enhanced Raman Scattering (SERS) Using Nanoparticles

Surface enhanced Raman spectroscopy (SERS) is one of the most promising label-free techniques for molecular sensing. In this chapter, we review the fundamental concepts of Raman spectroscopy and the need for SERS. We then discuss the fundamentals of SERS and focus on silver nanoparticles. This is followed by reviewing recent progress and applications of SERS. Finally, we discuss methods for further enhancing SERS signal using hollow core fibers.