Analyst Blog

Photonic crystal enhanced microscopy (PCEM) is a relatively new technique that utilizes a grating like substrate composed of a high refractive index material coating a low refractive index one. When irradiated with light at a resonant wavelength, this photonic crystal reflects all of the light, and is very sensitive to any changes on the surface.

Photonic Crystal Enhanced Microscopy of a nanoparticle on a photonic crystal

Researchers at the University of Illinois in the United States studied the effects of gold nanoparticles binding to  photonic crystals composed of a liquid epoxy polymer and TiO₂.  Although PCEM has been used to detect biological analytes without labels, they observed how a nanoparticle tag can reduce  the signal of a photonic crystal. Furthermore, they determined the distance required between the nanoparticles for detection, and this could be used in future amplification schemes such as in single molecule sensing.

To read more about this topic, click the link below. It will be free to read until February 28.

Single nanoparticle detection using photonic crystal enhanced microscopy
Yue Zhuo,  Huan Hu, Weili Chen,  Meng Lu,  Limei Tian,  Hojeong Yu, Kenneth D. Long,  Edmond Chow,  William P.   King, Srikanth Singamaneni  and  Brian T. Cunningham
Analyst, 2014, Advance Article
DOI: 10.1039/C3AN02295A

On-chip evaluation of platelet adhesion and aggregation

The use of nanoparticles in diagnostic and therapeutic roles requires that we understand their interactions and behaviour within complex biological systems. Where clinical applications would involve intravenous injection of nanoparticle-based therapeutics, it will be necessary to understand the interaction between nanoparticles and native blood components.

To address this issue, Christy Haynes and coworkers from the University of Minnesota, USA, have created a microfluidic device coated with endothelial cells to mimic the walls of the vascular system. This initial in vitro approach was carried out with both activated and unactivated platelets in the presence of various (therapeutically-relevant) concentrations of fluorescently-labelled, mesophorous silica nanoparticles. The impact of nanoparticles on the critical platelet functions of adhesion and aggregation was assessed.

Microfluidic platforms are readily customised and future work would be expected to expand upon these initial conditions to advance our understanding of nanotoxicology and interaction studies.

To read more about this study and the impact of nanoparticles on platelet interactions you can access this Analyst HOT Article free until 6 January 2014:

On-chip evaluation of platelet adhesion and aggregation upon exposure to mesoporous silica nanoparticles
Donghyuk Kim, Solaire Finkenstaedt-Quinn, Katie R. Hurley, Joseph T. Buchman and Christy L. Haynes 
Analyst, 2014, Advance Article
DOI: 10.1039/C3AN01679J

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