Shifted-Excitation Raman Difference Spectroscopy (Serds) In Forensics

INTRODUCTION

Raman spectroscopy is a powerful technique for non-destructive materials analysis, especially in forensic science. By measuring light scattered from a sample, Raman spectroscopy provides information about molecular vibrations, allowing the identification of drugs, explosives and other illegal substances. Raman spectroscopy requires very little sample preparation suitable for analyzing even a small sample.

The attenuation of unwanted Raman signals is a challenge for this application. However, for example, although water produces a strong signal in the infrared and can attenuate the signal of the actual analyte, it does not exhibit a strong signal in Raman spectroscopy. Aqueous solutions can therefore be analyzed directly without the complications of water obscuring analyte peaks, making the analysis of many types of forensic evidence containing water or moisture more desirable. Many hand-held or hand-held Raman spectrometers are now available, making them ideal for on-site forensic investigations. Since only a small fraction of the photons from the light source are scattered and only about one in ten million scattered photons participate in Raman scattering, the conventional/conventional Raman signal is inherently weak. In general, this is not an obstacle for bulk analysis and conventional Raman spectroscopy methods are sufficient for such samples, even when using handheld/portable instruments. However, analyzing trace evidence is challenging, requiring highly sensitive detection capabilities. Methods have been developed to generate much stronger Raman signals to achieve high sensitivity.

One such method is excitation-stimulated Raman difference spectroscopy (SERDS).

METHODS

Conventional Raman spectroscopy is a powerful and significant tool in forensic analysis. It can distinguish many types of body fluids, such as blood by gender, race, history, and distinguish maternal fluids by race and bones. Raman is also used to analyze questionable documents and other evidence.

Use a 785nm wavelength laser as the excitation source. And it is compared and evaluated as a promising method. However, for samples with weak conventional Raman signals, variable stimulation Raman difference spectroscopy (SERDS) can be used, which will help enhance the Raman signal.

Fluorescence is often considered the archenemy of Raman spectroscopy if any component (analyte, impurity, etc.) in the sample is fluorescent. As a result, a lot of effort has been devoted to solving this problem. Among the approaches/approaches developed to date, a relatively new method called shifted-stimulated Raman difference spectroscopy (SERDS) has been shown to be quite effective in removing fluorescence interference and other background noise in Raman analysis of some samples.

Eliminating fluorescence according to the Kasha-Vavilov principle, molecular luminescence can only result from relaxing the lowest excitation level to the ground state. Therefore, fluorescence is not affected by small changes in excitation wavelength (or wave number). However, the wavenumber of the Raman scattered photons changes with a change in the excitation wavelength (or wavenumber), even though the Raman shift (the difference in wavenumber between the excited photon and the scattered photon does not elastic) does not change. Therefore, theoretically, subtracting two spectra of the same sample obtained with slightly different excitation wavelengths (with Δλ typically no greater than 2 nm) can remove fluorescence interference in the absence of bleaching. optical, produces a Raman biased spectrum, which can be converted to a clean, background-free Raman spectrum by reconstruction operations. And use it as a useful tool in analyzing some forensic evidence.

Figure 1 . Difference between conventional Raman spectrum (top, red) and SERDS spectrum (bottom, blue) of cigarette lining paper.

A survey was conducted with 25 different cigarette brands, using SERDS to test cigarette wrappers. Two slightly different excitation wavelengths were used: 784 nm and 785 nm, respectively. Figure 1 shows the difference between conventional/conventional Raman spectra and SERDS spectra. In the conventional spectrum, most of the Raman peaks are obscured by fluorescence in the interferences with only the peaks at 1085 and 1507 cm −1 observable as highlighted. However, in addition to these two peaks, seven more characteristic Raman peaks were observed in the SERDS spectrum as highlighted, along with the flat baseline.

From the Raman spectrum information found above combined with a few algorithms, researchers can easily analyze the necessary desired characteristics of the evidence. 

APPLICATIONS

• Drug Identification: Spectroscopic techniques are utilized to identify illicit drugs and pharmaceuticals seized during criminal investigations.
• Forensic Trace Evidence Analysis: Spectroscopy is employed to analyze trace evidence such as fibers, hairs, and glass fragments found at crime scenes.
• Document Examination: Spectroscopic analysis is employed in document examination to detect alterations, forgeries, and counterfeit materials.

BUILD SYSTEM

INTINS can provide a complete system for this application. The Ocean HDX Raman spectrometer is a compact, high-performance spectrometer for 785 nm Raman excitation applications. This small-footprint instrument unlocks Raman signature data from 150 cm-1 to 3400 cm-1, is available with a 25 µm or 50 µm entrance slit, and can be combined with a laser, probe, and sample holder to measure solids, powders, and liquids.

HDX spectrometer is known as a series with high sensitivity. Responsive from 200 – 1100 nm with great sensitivity in the UV. Onboard buffering stores up to 50,000 time-stamped spectra so you will not miss a single data point. In addition, Ocean HDX utilizes a host of communication options including USB 2.0, Gigabit Ethernet, RS232, 802.11a/b/g/n WiFi and Access Point

WiFi.

Less expensive than traditional scientific-grade Raman instruments yet sacrificing very little in performance, Ocean HDX Raman is within reach to a wider range of users, including university teaching and research labs, budget-limited start-ups, and anyone that appreciates great value. In addition, Ocean HDX Raman is attractive for integration into other products, offering the advantages of small size and lightweight, plus thermal stability.

Intins offers a variety of 785 nm Raman lasers, commonly used in Raman spectroscopy. The 785 nm wavelength is particularly popular because it offers a good balance between fluorescence suppression (common with shorter wavelengths) and Raman signal intensity (which decreases with longer wavelengths).

These lasers are designed to provide a stable and precise 785 nm wavelength, which is essential for high-precision Raman measurements. Raman lasers also provide different output power levels to suit each user's specific application. It is designed to integrate seamlessly with Ocean Insight's wide range of Raman spectrometers and accessories.

CONCULATION

Raman spectroscopy is an extremely useful tool for performing analytical techniques in forensics. The development of more advanced Raman methods with Raman signal enhancement promises to make forensic evidence analysis much more sensitive, accurate, and timely. Along with the development of increasingly advanced science and technology, Raman spectroscopy is increasingly and widely deployed in the field of forensic science.