A new highly adaptable design of shear-flow device for orientation of macromolecules for Linear Dichroism (LD) measurement.

This article presents a new design of flow-orientation device for the study of bio-macromolecules, including DNA and protein complexes, as well as aggregates such as amyloid fibrils and liposome membranes, using Linear Dichroism (LD) spectroscopy. The design provides a number of technical advantages that should make the device inexpensive to manufacture, easier to use and more reliable than existing techniques. The degree of orientation achieved is of the same order of magnitude as that of the commonly used concentric cylinders Couette flow cell, however, since the device exploits a set of flat strain-free quartz plates, a number of problems associated with refraction and birefringence of light are eliminated, increasing the sensitivity and accuracy of measurement. The device provides similar shear rates to those of the Couette cell but is superior in that the shear rate is constant across the gap. Other major advantages of the design is the possibility to change parts and vary sample volume and path length easily and at a low cost.

Quantitative enhanced Raman scattering of labeled DNA from gold and silver nanoparticles.

Surface-enhanced resonance Raman scattering (SERRS) from silver nanoparticles using 514.5-nm excitation has been shown to offer huge potential for applications in highly sensitive multiplexed DNA assays. If the technique is to be applied to real biological samples and integrated with other methods, then the use of gold nanoparticles and longer wavelengths of excitation are desirable. The data presented here demonstrate that dye-labeled oligonucleotide sequences can be directly detected by SERRS using gold nanoparticles in a quantitative manner for the first time. The performance of gold and silver nanoparticles as SERRS substrates was assessed using 514.5-, 632.8-, and 785-nm excitation and a range of 13 commercially available dye-labeled oligonucleotides. The quantitative response allowed the limit of detection to be determined for each case and demonstrates that the technique is highly effective, sensitive, and versatile. The possibility of excitation at multiple wavelengths further enhances the multiplexing potential of the technique. The importance of effectively combining the optical properties of the nanoparticle and the dye label is demonstrated. For example, at 632.8-nm excitation, the dye BODIPY TR-X and gold nanoparticles make a strong SERRS combination with very little background fluorescence. This study allows the choice of nanoparticle and dye label for particular experimental setups, and significantly expands the applicability of enhanced Raman scattering for use in many disciplines.