Julio C. Alvarez
 |
Assistant professor |
Education
B.S., Universidad del Tolima, Ibague, Colombia, 1989
M.S., Universidad del Valle, Cali, Colombia, 1996
Ph.D., University of Miami, Coral Gables, Fla., 2000
Postdoctoral Research, Texas A&M University, College Station, Texas, 2000-2004
Research interests
The research in our group revolves around using electrochemistry and surface chemistry to address different chemical and electrochemical problems. We use platforms containing micro and nanoscopic domains (e.g. microfluidics, lab-on-chip, nanoparticles) to implement chemical principles that allow us to tackle the problems we are interested in. Despite the emphasis in electrochemistry and surface chemistry, this research provides a wide framework for the education of students and postdocs encompassing a broad range of chemical and physical concepts. The specific projects that are currently under way in our laboratory are as follows.
New strategies for enhancing sensitivity and selectivity in electrochemical detection
In this project we use chemical coupling between two electrochemical reactions to enhance the sensitivity or selectivity of a target reaction while using a second reaction as an activator. The activator reaction has the role of shifting the redox potential of the target reaction so that the latter can be detected in conditions in which otherwise it would be undetectable and/or other redox species would not interfere. We can implement this strategy by taking advantage of the flow and multiple electrode capability available in microfluidic systems or in conventional electrochemical cells using sequential pulsing techniques. The redox potential shift is a thermodynamic or kinetic effect induced by the electrogenerated products of the activator reaction. Initially, we have proved this notion with electrochemical reactions generating protons, but the principle is of general scope and can be implemented with any pair of reactions sharing a common chemical and provided that both reactions can be mixed within the time scale of the experiment.
Kinetic and thermodynamic facilitation of electrochemical reactions by chemical coupling
The objective of this project is to use the chemical coupling principle discussed above to facilitate kinetically or thermodynamically electrochemical reactions of technological relevance. We want to learn how to make an electrochemical reaction faster (electrocatalysis) or easier (redox potential shift) by chemically coupling a second reaction. The chemicals producing favorable thermodynamic or kinetic effects on a target reaction are electrogenerated in-situ or attached to the electrode surface depending on the approach. These reagents can induce a shift in the redox potential or provide a transition state of lower energy such that the target reaction occurs at an easier redox potential or at a faster rate. We use electrochemical reactions such as quinone reduction, catechol oxidation, and other reactions with rich coupling chemistry (proton transfer, group transfer, bond braking, etc.), as models to implement these principles. But the ultimate goal is to involve technologically important reactions like oxygen reduction and nitrogen fixation.
Enhancement of catalytic activity of nanoparticles by chemical coupling
Many redox reactions are catalyzed by nanoparticles, which can behave similarly to macroscopic electrodes by exchanging electrons with molecules that react at the nanoparticle surface. Their redox potential depends greatly on the nanoparticle material, its size and its local chemical environment. We utilize chemicals in solution or adsorbed on the nanoparticle surface to shift the redox potential of the nanoparticle or provide a lower energy for the transition state of a target reaction. The goal in this case is to use chemical coupling to facilitate the target reaction thermodynamically or kinetically.
Electrochemical detection of non-electroactive species
The goal of this project is to detect electroinactive bioprobes such as proteins, viruses, bacteria, etc., using electrokinetic methods in microfluidic systems. Initially, we have detected proteins and small non-electroactive species using streaming potentials measurements. Streaming potentials are charge gradients spontaneously generated when liquids are forced through microchannels and can be measured with two electrodes and a voltmeter along the flow direction. The magnitude of this potential difference is proportional to the liquid pressure and its relative sign is given by the surface charge of the channel. The principle implemented here relies on using a microchannel surface with positive charge to detect proteins negatively charged that adsorb on the channel surface. The reverse case is also possible and the detection limits are in the nanomolar and micromolar level depending on the molecule, however, further optimization of the sensitivity and selectivity of this method is currently under way in our laboratory. The key aspect that makes this work unique in comparison with previous research in streaming potentials, is the combination of materials, surface modification strategies and the effective use of pressure-driven flow and surface charge to elicit a simple sensing principle. This detection method does not require analyte labeling (fluorescent, redox or radioactive) and any species interacting/adsorbing with a surface and inducing a charge change could be detected. Because of the simplicity of the approach, this method could lead to portable and simple-to-operate sensors useful in on-field applications.
Publications
Khalid, I. M.; Pu, Q.; Alvarez, J. C.; “Thermodynamic and Kinetic Enhancement of Electrochemical Sensitivity by Chemical Coupling in Microfluidic Systems.” Angew. Chem. Int. Ed., 2006, 45, 5829-5834.
Pu, Q.; Oyesanya, O.; Thompson, B.; Liu, S.; Alvarez, J. C.; “On-Chip Micropatterning of Plastic (Cyclic Olefin Copolymer, COC) Microfluidic Channels for the Fabrication of Biomolecule Microarrays Using Photografting Methods.” Langmuir, 2007, 23, 1577-1583.
Pu, Q.; Alvarez, J. C.; “Label-Free Detection of Proteins and Small Molecules by Streaming Potential Measurements in Plastic Microfluidic Chips Using Tailored Modification of the Microchannel Surface.” 2007, submitted.
Pu, Q., Alligrant, T., Alvarez, J. C., Faulconer, E., Farhi, J., Hurt, V.; “Monitoring Surface charge in Capillaries by Streaming Potentials: An easy Experiment for High School Seniors and Freshmen Students.” 2007, submitted.
