Chemistry

Home » Analytical Chemistry » Page 2

Analytical Chemistry

Sharma Lab Published in Analytical Chemistry and Analyst

by

The Sharma Raman Lab published their work “Direct Surface Enhanced Raman Spectroscopic Detection of Cortisol at Physiological Concentrations” in Analytical Chemistry.

Josh Moore is the first author on this piece and recently earned his PhD in the Chemistry program.

Cortisol is an important steroid hormone in vertebrate physiology and plays a role in acute and chronic stress response. Current methods for determination of cortisol concentrations in biofluids require extensive sample preparation and long run times. Raman spectroscopy is an attractive alternative because analysis is rapid and non-destructive to the sample.

The Sharma Lab has developed a surface-enhanced Raman spectroscopy (SERS)-based method for detection of cortisol in ethanol that shows a sigmoidal concentration response and a limit of detection of 177 nanomolar, which is in the physiologically relevant range. The method can be applied to more complex solvent environments through the use of multivariate analysis techniques, where principal components analysis (PCA) demonstrates a linear separation according to cortisol concentration in a serum mimic. “We are, to our knowledge, the first group to report on the detection of cortisol using label-free SERS, which does not require a Raman reporter molecule to obtain signal,” Moore said.

The Sharma Lab published their work “Surface-enhanced spatially-offset Raman spectroscopy (SESORS) for detection of neurochemicals through the skull at physiologically relevant concentrations” in Analyst. 

Detection techniques for neurotransmitters that are rapid, label-free, and non-invasive are needed to move towards earlier diagnosis of neurological disease. Surface-enhanced Raman spectroscopy (SERS) allows for sensitive and selective detection of target analytes. The combination of SERS with spatially offset Raman spectroscopy (SORS) in a technique termed surface enhanced spatially offset Raman spectroscopy (SESORS) permits a sensitive and selective detection of neurotransmitters through the skull.

In this piece, the group presents the SESORS detection of individual neurotransmitters and mixtures of neurotransmitters at physiologically relevant concentrations, while also establishing limits of detection.

Calhoun Lab Illuminates ‘Dark’ States in Nano Letters Paper

by

Researchers in the Department of Chemistry at the University of Tennessee, Knoxville, are shooting lasers at quantum dots to illuminate ‘dark’ states and provide new insights that can steer the design of future materials.

Tiny crystals known as quantum dots have become so ubiquitous that you can find them in modern commercial televisions. Yet there are still key questions that have remained unanswered despite decades of research about how these crystals work. In particular, it is not clear exactly how the surfaces of quantum dots affect how they interact with light.

When light hits a quantum dot, the energy is stored in energy levels or states. When this energy moves to states on the surface of the quantum dot, it becomes “trapped” and lost for potential use. These surface states, however, are invisible to basic optical experiments because they cannot directly absorb the light, and this leaves the energies of these surface states unknown.

That was until a collaborative UT/Oak Ridge National Laboratory research team, led by Tessa Calhoun in the University of Tennessee’s Department of Chemistry, developed a new way to shed light on them. Their electronic sum frequency generation microspectroscopy technique simultaneously mixes different colors of ultrashort laser pulses to generate new colors of light that describe these elusive ‘dark stats’ on the quantum dots and is detailed in their recent paper published in Nano Letters.

“I was excited by just how many energy levels we could detect with a single measurement at ambient conditions,” Calhoun said.

In addition to being able to match dozens of known energy levels from literature, their studies were able to detect multiple elusive surface states.

“While many other experiments had suggested the presence of one or more of these states, we are the first to be able to directly show that there is more than one surface state in these quantum dots.” Calhoun said.

In addition to Calhoun, other team members were Brianna Watson, the lead author, and Benjamin Doughty, a staff scientist in the Chemical Sciences Division at ORNL. Brianna was a graduate student in the UT Department of Chemistry and is now conducting postdoctoral research using microscopy at Boston Children’s Hospital.

This new information about the energies of dark states promises to provide an avenue to control these generally undesirable defects to improve performance in devices.

Knowing more about these surface states will allow scientists to design better nanoparticles and Calhoun’s group is excited for the future systems they can explore with their new microspectroscopy.

Read more about this research in the paper titled “Energetics at the Surface: Direct Optical Mapping of Core and Surface Electronic Structure in CdSe Quantum Dots using Broadband Electronic Sum Frequency Generation Microspectroscopy.”