Research
Our lab focuses on the development of biosensors and biosensing methods based on surface-enhanced Raman scattering (SERS). We take advantage of our expertise in spectroscopy, nanotechnology and synthetic biology to try to solve critical issues in diagnostics and environmental analysis.
Why biosensors?
Biosensors are composed of a biological recognition element and a transduction mechanism. The recognition is used to specifically bind to a target biomolecule and the transduction will translate the binding to a response that can be detected by interrogating the sensor. Our sensors use SERS as a transduction mechanism.
The power of biosensors resides in the ability to perform the same work that is perform in full-scale analytical labs (i.e., identifying a specific target molecule) but within a single nanoscopic tool. Biosensors enable applications, such as continuous in vivo monitoring, point-of-care diagnostic tests and remote pollutant analysis.
In our lab, we specifically use reagentless SERS sensors. Reagentless (or homogeneous) means that they do not require any additional processing step to work. They encounter the target analyte and turn “on”. To this end, we use functional nucleic acid that change shape in the presence of the target analyte. For the meaning of SERS, see below.
Why SERS?
Surface-enhanced Raman scattering (SERS) is a phenomenon associated with the interaction of light with matter at the nano-size. Metallic nanoparticles can function as antennas and amplify the scattering of molecules near their surface. This phenomenon can be utilized as a transduction mechanism in nanosensors by either directly measuring the scattering of analytes on the surface of nanoparticles (direct or intrinsic SERS) or by using receptor-reporter systems to measure binding of analytes to receptors (indirect or extrinsic SERS). Our lab takes advantage of both mechanism in different applications.
A significant advantage of SERS over other transduction mechanism is the possibility for highly multiplexed analysis (i.e., simultaneous detection of multiple analytes). This advantage is due to the vibrational nature of Raman and SERS. While a fluorescence emission peak spans across 50-100 nm of the electromagnetic spectrum, a single SERS peak is roughly 1 nm wide, making it possible to observe many peaks in a single spectrum.
Our research divides roughly into the three following branches:
Design of SERS biosensors using rational and inverse design -1-
SERS holds immense potential for ultrasensitive molecular detection. However, current biosensing methods have limited sensitivities, possible target molecules and multiplexing capabilities. We advancing the way we design these sensors to improve and fully take advantage of these features, using rational design principles and inverse design based on machine learning.
Our lab has designed a catalytic sensing mechanism that amplifies the response of reagentless sensors. The principle for this mechanism were then used in a sensor design algorithm that permits to generate the functional nucleic acid sequences to use in the biosensor. In the future, we plan to use this initial form of automation and additional automation to build large dataset of biosensors data. These data will permit us to use machine learning to understand key aspects in the sensor design (e.g., specific sequences and features).
Our lab has also designed a protocol to extend the use of reagentless SERS sensors from genetic target to small molecules. These sensors use aptamers as recognition elements for small molecules, taking advantage of a similar functional nucleic acid mechanism.
Our current work focuses on the introduction of automation in the biosensor lab workflow for the generation of large dataset, which will be pivotal in the development of inverse design approaches.
Translation of SERS biosensors for point-of-need and field-ready applications -2-
Most SERS sensing applications are designed to work in solution or on a substrate. While these methods are powerful, they are primarily suited to work in lab settings. We are working on multiple projects involving the development of solution to apply the sensors at the point of need.
We have developed a SERS sensing hydrogel that integrate our reagentless sensors into a hydrogel material. These sensing materials can be used to detect targets by contact. We established the use of these materials to detect infections in plants by putting the hydrogel in contact with a leaf. Current work is pushing the use of these materials to other applications, including detection of pesticides and food contaminants, as well as translating these tests to work directly in the field -literally-.
We are developing strategies to store and use our sensors on demand. Reagentless SERS sensors are used in solution but, when stored in solution, they lose signal over time due to irreversible degradation processes. We have tested the use of lyophilization on these sensors to improve storage and use, as lyophilized sensors can be used by simple addition of sample solution to them. We are currently exploring the development of assay tablets to perform all assay steps in a single solution without any processing steps, other than the tablet addition.
Remote sensing remains hard to achieve with SERS due to the requirement for nanoparticle to be in contact with the sample. To overcome this issue, we are working on the design of fiberoptics-based sensors, placing reagentless sensors at the end of an optical fiber. This strategy permits to access samples to perform continuous monitoring, without having to sample. For example, this solution would permit to detect contaminants in environmental waters continuously.
In collaboration with the engineering department at UC, we are also working on the design of lateral-flow assay (LFA) systems -the at-home COVID test is an LFA, for example-. We are substituting the common nanomaterials used in these tests (gold nanoparticles) with nanomaterials modified and optimized to give strong SERS signal (functionalized nanostars). This strategy has permitted the improvement of the sensitivity and quantification capability of these tests of multiple orders of magnitude, opening the possibility for new interesting applications.
Advanced SERS analysis of biological samples -3-
The projects described above take advantage of biosensors and extrinsic SERS; however, intrinsic/direct SERS has also many advantages. We are using this method (direct SERS) to develop ways to quickly and simply analyze biological samples. The SERS spectrum of a biological sample is due to all molecules interacting with the SERS substrate/nanostructure. These spectra can be very complex but in principle they carry all the information about the biological sample molecular composition. To understand these spectra, we use multivariate analysis of different kind and analyze spectra from various biological samples. In collaboration with the biomedical engineering department, we are working on the analysis of exosome samples derived from patients’ blood, to perform non-invasive cancer screening. In collaboration with P&G, we work on analysis of bacteria sample, to perform a quick monitoring of bacteria culture status. These applications have shown that with SERS/Raman not only we can perform diagnostic classifications, but we can also learn chemical insight about differences between biological samples under analysis.
Additionally, our lab is also interested in the use of Raman in heritage science efforts:
Raman spectroscopy and spatially offset Raman scattering (SORS) for heritage science applications
We have previously worked with the Cincinnati Art Museum to identify the originality of multiple parts of an artifact and we are currently collaborating with the Institute of Heritage Science in Milan, to design new systems for in-situ sub-surface Raman analysis of artwork.
We thank the following entities for supporting our research work:
