Leonardo R. Allain

Development of a Portable Raman Spectrometer for Medical Diagnostics

This paper describes a self-contained, portable Raman instrument that has been developed for biomedical analyses. The instrument consists of a 785-nm diode laser for excitation, an acousto-optic tunable filter (AOTF) for wavelength discrimination, and an avalanche photodiode for detection. The primary component of this system is the AOTF and it has been selected based on its spectral range along with its high resolution, approximately 7.5 cm-1. Software has been developed in-house in the programming language of C for controlling the instrument (i.e., the AOTF frequency, the signal acquisition, etc.). Evaluation of this instrument has been performed by analyzing several standard samples and comparing their spectra to spectra acquired using a conventional laboratory system. In addition to system evaluation, this paper will also discuss potential applications of this instrument to multiplexed genechip types of analyses.

Iron(III)-Mediated Oxidative Degradation on the Benzylic Carbon of Drug Molecules in the Absence of Initiating Peroxides

Metal ions play an important role in oxidative drug degradation. One of the most ubiquitous metal ion impurities in excipients and buffers is Fe(III). In the field of oxidative drug degradation chemistry, the role of Fe(III) has been primarily discussed in terms of its effect in reaction with trace hydroperoxide impurities. However, the role of Fe(III) acting as a direct oxidant of drug molecules, which could operate in the absence of any hydroperoxide impurities, is less common. This work focuses on Fe(III)-induced oxidation of some aromatic drug molecules/drug fragments containing benzylic C-H bonds in the absence of initiating peroxides. Alcohol and ketone degradates are formed at the benzylic carbon atom. The formation of a π-stabilized cation radical is postulated as the key intermediate for the downstream oxidation. Implications are briefly discussed.

SERS gene probe for DNA diagnostics

We describe the development of a surface-enhanced Raman scattering gene (SERGen) probe technology for rapid screening for diseases and pathogens through DNA hybridization assays. The technology combines the use of gene probes labeled with SERS-active markers, and nanostructured metallic platforms for inducing the SERS effect. As a result, SERGen-based methods can offer the spectral selectivity and sensitivity of SERS as well as the molecular specificity of DNA sequence hybridization. Furthermore, these new probe s preclude the use of radioactive labels. As illustrated herein, SERGen probes have been used as primers in polymerase chain reaction (PCR) amplifications of specific DNA sequences, hence further boosting the sensitivity of the technology. We also describe several approaches to developing SERS-active DNA assay platforms, addressing the challenges of making the SERGen technology accessible and practical for clinical settings. The usefulness of the SERGen approach has been demonstrated in the detection of HIV, BRCA1 breast cancer, and BAX genes. There is great potential for the use of numerous SERGen probes for multiplexed detection of multiple biological targets.

Biochip using a biofluidic system for detection of E. coli and other pathogens

This work provides an overview of progress made, in our laboratory, towards the development of a practical biochipbased technology with a biofluidics system for the detection of E. coli and other pathogens. Efforts have been devoted towards efficient coupling between a compact biofluidics sample/reagent delivery system and an integrated circuit (IC) biochip, consisting of a 2-dimensional photosensor array, for on-chip monitoring of bioassays. The complementary metal-oxide semiconductor (CMOS) technology has been implemented to design and produce the IC biochip, which features a 4x4 array of independently addressable photodiodes that are integrated with amplifiers, discriminators and logic circuitry on a single platform. The CMOS-based biochip offers the advantages of compactness and low power consumption, making it better suited for field use than other array detectors, including CCDs. The biofluidics system includes a 0.4 mL hybridization chamber, which accommodates disposable sampling platforms embedded with bioreceptors for selective capture of pathogen DNA, proteins, or antibodies in discrete zones. The independently operating photodiodes of the IC biochip offer the capability of monitoring of multiple assays. Highlights of this work include highly sensitive detection of E. coli (<50 organisms) and quantitative capability with a linear dynamic range of 3-5 orders of magnitude for various assays.