Analyst Blog

Data sub-selection in transmission Raman spectroscopy

The analysis of compound mixtures in powder and tablet form has a range of purposes, from monitoring the stability of a formulation over time and quality control of a product, to the forensic analysis of illicit substances. Transmission Raman spectroscopy is a promising candidate for this type of analysis. TRS is fast and non-destructive, it produces data that is easy to interpret, and has good penetration depth for opaque samples such as powders.

Researchers led by Jonathan Burley at the University of Nottingham (UK) have investigated ways to improve the accuracy of TRS for quantitative analysis. In this HOT Analyst paper, they report the first detailed analysis of data sub-selection for a set of transmission Raman data obtained from a model pharmaceutical formulation. Burley and co-workers also focus on the utility of low-wavenumber data, which has only become accessible in recent years. The authors anticipate that their findings may shape the future development of Raman instrumentation.

To read more about this work, please access the link below. This paper will be free to read until 6 January 2014.

Quantification of pharmaceuticals via transmission Raman spectroscopy: data sub-selection
Jonathan C. Burley, Adeyinka Aina, Pavel Matousek and Christopher Brignell
Analyst, 2014,139, 74-78
DOI: 10.1039/C3AN01293J

The rapid and specific detection of pathogenic bacteria, such as staphylococci, is an important worldwide concern. Staphylococci cause serious infections in humans and animals and certain species such as S. aureus and methicillin resistant S. aureus (MRSA) are developing antibiotic resistance that is quickly becoming a global crisis. The ability to detect these bacteria rapidly and in situ would allow for early treatment even in countries with poor access to healthcare.

Immobilized phage proteins for specific detection of staphylococci

Canadian researchers from McGill University and Polytechnique Montreal have recently shown the use of immobilized bacteriophage proteins to develop a biosensor for the specific detection of 8 clinical isolates of staphylococci. Hicham Chibli and coworkers examined several purified phage proteins from the Endolysin class of enzymes and exploited their ability to specifically bind staphylococci. Indeed these immobilized phage proteins did not bind to other closely related bacteria.

Bacteriophages have been used as recognition elements for biosensors before, but this research shows the use of specific phage proteins instead of whole bacteriophages. “Compared with whole phages, these single proteins are smaller, easier to purify, and easier to assemble in a reproducible manner of a surface” – says Jay Nadeau of McGill University – “The small size is key for development of some types of biosensors where sensitivity is dependent upon thickness of the functionalizing layer, for example, microresonators” – he adds. The ability to develop microresonators with specific detection can provide small, portable and specific biosensors for in field use.

To know more about this study, please access the link below. This paper will be free to read for the next three weeks.

Immobilized phage proteins for specific detection of staphylococci
Hicham Chibli, Hala Ghali, Soonhyang Park, Yves-Alain Peter and Jay L. Nadeau  
Analyst, 2014, 139, 179-186
DOI: 10.1039/C3AN01608K

FTIR spectra of hormones triiodothyronine, thyroxine, diiodotyrosine, tyrosine and thyroid tissue

The combination of vibrational spectroscopy with mapping and imaging techniques to address important biochemical questions is an area of active and expanding research.  By subjecting adjacent tissue sections to standard histopathological screening and spectroscopic imaging, a greater understanding of the biochemical processes underlying tissue form and function can be achieved.

Researchers from Northeastern University, USA, and the Institute of Energy and Nuclear Research (IPEN), Sao Paolo, have used Fourier transform infrared (FTIR) microspectroscopy to examine healthy thyroid tissues. FTIR allows spatially resolved images, or maps, to be obtained by use of focal plane array detectors and spectral processing of the data then reveals chemical images.  In this HOT Analyst paper, Denise Zezell and coworkers present an example from their investigation of 80 different patient samples, which were analysed by transflection-mode FTIR mapping.  The approach was  applied to the study of healthy thyroid tissue and, with reference to thyroid specific hormones, iodination state. 

To know more about this research, click on the links below. This paper will be free to read for the next three weeks:

The characterization of normal thyroid tissue by micro-FTIR spectroscopy
Thiago M. Pereira, Denise M. Zezell, Benjamin Bird, Milos Miljković and Max Diem
Analyst, 2013,138, 7094-7100
DOI: 10.1039/C3AN00296A

Spectroscopic analysis of mycolic acid profiles

In bacterial-based diagnostics, the bacteria can evolve over time and it is important to be able to differentiate between multiple strains. Mycobacterium tuberculosis, which is responsible for causing tuberculosis (TB), has multiple drug-resistant strains. The most accurate method to identify toxic strains of TB, high performance liquid chromatography (HPLC), requires fluorescent labeling and extraction of the mycolic acids, from the outer membrane of the bacteria.

Researchers at the University of Georgia in the United States wanted a more direct detection method and approached this problem in two important aspects. They began by identifying the high molecular weight lipids within the bacteria using HPLC, gas chromatography (GC), and nuclear magnetic resonance (NMR) for several TB bacterial strains. NMR in particular was very important in identifying the structures of mycolic acids. Using the information from these techniques and surface enhanced Raman spectroscopy (SERS), they chemically classified the mycolic acid from both TB and non-TB strains. The SERS spectra underwent further statistical analysis and accurately identified different strains of TB label-free and with high sensitivity.

To know more about this research, click on the link below. This paper will be free to read for the next three weeks.

Identification of mycobacteria based on spectroscopic analyses of mycolic acid profiles
Omar E. Rivera-Betancourt, Russell Karls, Benjamin Grosse-Siestrup, Shelly Helms, Frederick Quinn and Richard A. Dluhy
Analyst, 2013,138, 6774-6785
DOI: 10.1039/C3AN01157G

LED-SERDS in Raman Spectroscopy

Raman spectroscopy finds a range of uses in analytical chemistry. Like infra-red (IR) spectroscopy it can provide a vibrational fingerprint by which compounds may be identified. Unlike IR, Raman is a scattering technique that does not require complex sample preparation, and water can be used as a solvent. In some samples, however, the Raman spectrum is rendered useless by intense fluorescence signals.

Chemical engineers Renata Adami (University of Salerno, Italy) and Johannes Kiefer (University of Aberdeen, UK) have developed a new approach to shifted-excitation Raman difference spectroscopy (SERDS) for suppression of fluorescence. SERDS experiments conventionally require expensive diode lasers, but in this Analyst paper Kiefer and Adami demonstrate the use of light-emitting diodes (LEDs) as an inexpensive light source. A dielectric bandpass filter narrows and stabilises the broad LED spectrum to make it usable for SERDS. While the resulting spectral resolution is low, different compounds and functional groups can be clearly distinguished using this method.

To read the full access, please click on the link below. This paper will be free to read for the next three weeks:

Low cost webcam based prism spectrometer

Techniques such as cavity ring-down spectroscopy (CRDS) have greatly enhanced the sensitivity in traditional absorption spectroscopy methods. Although CRDS can detect analytes in very small concentrations in solution, it requires expensive and complex instrumentation, which has restricted its widespread implementation. Alternatively, broadband cavity enhanced absorption spectroscopy (BBCEAS) has emerged to overcome some of these limitations. These adjustments allow for multiplexed data collection and improved resolution.

Researchers at the University of Cambridge, UK,  have constructed a BBCEAS apparatus using relatively simple components and achieved sensitivity levels similar to much more expensive systems.  Using a well-studied process, the Griess Assay, they measured different concentrations of nitrite and the dye Rhodamine 6 G with a system that contained a low cost prism spectrometer and a webcam detector. The limits of detection were found to be 3.7 nM (nitrite) and 850 pM (Rhodamine), and by adding a better detector, these can further be improved upon.

To read the full article, please access the link below. This paper will be free to read for the next three weeks:

High sensitivity liquid phase measurements using broadband cavity enhanced absorption spectroscopy (BBCEAS) featuring a low cost webcam based prism spectrometer
Zhechao Qu, Julia Engstrom, Donald Wong, Meez Islam and   Clemens F. Kaminski
Analyst, 2013,138, 6372-6379
DOI: 10.1039/C3AN01441J

Analysis of intracellular enzyme activity by SERS

Enzymatic activity in cells has been revealed by surface enhanced Raman scattering (SERRS) spectroscopic studies, according to new research led by Duncan Graham at the University of Strathclyde.

X-Gal, a SERRS inactive precursor and a common marker for galactosidase enzymes, was introduced to macrophage cells along with metal nanoparticles. On incubation, enzymatic activity of galactosidase on X-Gal produces a SERRS active trans-alkene dimerised product. This product adsorbs onto the delivered citrate capped gold nanoparticles producing a distinctive SERRS signal. Using SERRS mapping to evaluate the formation of this product, enzyme activity was assessed, not only across a cell population, but also at sub-cellular levels. The authors note that the SERRS activity in this study may not reflect the only sites of galactosidase activity, but rather the sites where both galactosidase and the nanoparticles are co-located. Nevertheless, approaches towards sub-cellular analysis of enzyme activity are important.

Advances in targeted nanoparticle uptake combined with the multiplexing capability of SERRS make this an interesting approach to sub-cellular studies of biochemical activity.

To read the full article, please click on the link below. This paper will be free to read until October 18th.

Analysis of intracellular enzyme activity by surface enhanced Raman scattering
Ross Stevenson, Sarah McAughtrie, Laura Senior, Robert J. Stokes, Helen McGachy, Laurence Tetley, Paola Nativo, James M. Brewer, James Alexander, Karen Faulds and   Duncan Graham
Analyst, 2013, Advance Article
DOI: 10.1039/C3AN00729D

Take a look at these new HOT articles just published in Analyst! These papers will be free to read for the next three weeks. Download them today!

The global identification of tRNA isoacceptors by targeted tandem mass spectrometry
Collin Wetzel and Patrick A. Limbach  
Analyst, 2013,138, 6063-6072
DOI: 10.1039/C3AN01224G

Extraction and separation of proteins by ionic liquid aqueous two-phase system
Xiao Lin, Yuzhi Wang, Qun Zeng, Xueqin Ding and Jing Chen  
Analyst, 2013, Advance Article
DOI: 10.1039/C3AN01301D

A smart T1-weighted MRI contrast agent for uranyl cations based on a DNAzyme–gadolinium conjugate
Weichen Xu, Hang Xing and Yi Lu  
Analyst, 2013, Advance Article
DOI: 10.1039/C3AN01182H

Improved analysis of oligosaccharides for matrix-assisted laser desorption/ionization time-of-flight mass spectrometry using aminopyrazine as a derivatization reagent and a co-matrix
Yan Cai, Ying Zhang, Pengyuan Yang and Haojie Lu
Analyst, 2013, Advance Article
DOI: 10.1039/C3AN01228J

A chemical quenching- and physical blocking-based method to minimize process-mediated aggregation of antibody-crosslinked nanoparticles for imaging application
Chandra K. Dixit, Shibsekhar Roy, Conor Byrne, Richard O’Kennedy and Colette McDonagh  
Analyst, 2013, Advance Article
DOI: 10.1039/C3AN01294H

Exploring the electrochemical performance of graphitic paste electrodes: graphene vs. graphite
Luiz C. S. Figueiredo-Filho, Dale A. C. Brownson, Maria Gómez-Mingot, Jesús Iniesta, Orlando Fatibello-Filho and Craig E. Banks  
Analyst, 2013, Advance Article
DOI: 10.1039/C3AN00950E

An investigation into the simultaneous enzymatic and SERRS properties of silver nanoparticles
Kristy S. McKeating, Sian Sloan-Dennison, Duncan Graham and Karen Faulds  
Analyst, 2013, Advance Article
DOI: 10.1039/C3AN01451G

Electrochemical piezoelectric-excited millimeter-sized cantilever (ePEMC) for simultaneous dual transduction biosensing
Blake N. Johnson and Raj Mutharasan  
Analyst, 2013, Advance Article
DOI: 10.1039/C3AN01353G