Dedicated to finding a pattern of facts

Chen’s group is dedicated to developing methods for characterizing a diverse range of materials, including DNA, proteins, polymers, ceramics, semiconductors, and metals, with a particular emphasis on surface and interfacial chemistry. Their primary focus is on the use of spectroscopy and microscopy techniques to better understand the performance of these materials in applications such as biosensing, nanodevices, and solar cells. Additionally, the group is committed to advancing computational software for the analysis of data derived from these measurements, particularly in the context of reaction kinetics.

Key contributions from the group include groundbreaking work on reaction kinetics, such as the theory of single-molecule adsorption kinetics, quantum dot surface reaction mechanisms, click chemistry kinetic models, mixed halide perovskite phase separation kinetics, COVID-19 kinetics, biophysics of dye-DNA interactions, and surface functionalization strategies. One notable example is Chen’s proposed kinetic model for the adsorption of diffusion-limited molecules from bulk solution to target molecules immobilized on a surface, a fundamental process in heterogeneous reactions. Despite over 200 years of research by many distinguished scientists, this phenomenon has remained a challenge. In his 2022 papers published in AIP and JPCA, Chen introduced a fractional reaction kinetic model that offers a novel and nonintuitive approach, one that is robustly supported by experimental data.

The fractional reaction order arises because the displacement of molecules during diffusion depends non-linearly on time, which contrasts with the linear relationships typically observed in everyday movement. Chen introduces the concept of an "adsorption cross-section" for the first time, which could serve as the sole free parameter in calculating the adsorption rate for a given system. This innovative theory paves the way for applications across various fields, including biology, environmental science, industrial reaction kinetics, and battery technology. 

External Fund

NIH R15 2018-2022, Program officer: Dr. Michael Smith

NIH R15 2023-2026 (continued), Program officer: Dr. Lisa H. Chadwick

Title: Super-resolution optical mapping for DNA analysis using triplex-forming oligonucleotides as stochastic molecular probes.

Sponsor: National Human Genome Research Institute (NHGRI), National Institute of Health (NIH).

NSF 2020, MRI: Acquisition of a Matrix-assisted Laser Desorption/ionization Time-of-flight Mass Spectrometer to Enhance Research and Education.

Projects

As experimental physical chemists, our primary goal is to develop and apply advanced techniques to understand the complex behavior of molecules and nanoparticles at surfaces and interfaces. This research aims to drive the development of new materials and technologies that can enhance and improve our lives. 

Single Molecule Kinetics

We develop molecular probes for single-DNA imaging and synthesize a range of nanoparticles and quantum dots for photoluminescence measurements and nanodevice fabrication. Using super-resolution fluorescence microscopy, single-molecule diffusion and binding kinetics, single-molecule FRET kinetics, and single-particle fluorescence dynamics. Statistical methods are employed to analyze these data. The figure illustrates examples of Monte Carlo simulations applied to the adsorption of molecules on a surface, using both 1D and 3D models. Additionally, we are developing MATLAB code for data analysis, fitting, and simulations across various kinetic systems, including smFRET, reaction kinetics, and diffusion processes. 

Materials Science

Our group made thin-film solar cells and measured their interfacial chemical and electrochemical properties. The figure above shows a perovskite solar cell (PSC) fabricated and tested in our lab in 2018 by graduate student Juvinch Vicente, achieving over 15% efficiency under AM 1.5G standard sunlight illumination. PSCs represent a promising next-generation solar technology breaking the efficiency record of solar cells.

We also synthesized perovskite quantum dots and investigate their photoluminescent properties, particularly under varying conditions and passivation treatments. About photo shows a set of mixed-halide perovskite quantum dots synthesized by graduate student Pavithra Ariyaratne with different fluorescent emission colors. These materials show great potential for applications in light-emitting diodes (LEDs), lasers, and display screens.

Collaborators

Internal Fund (Ohio University)

2023 NQPI Research Challenge Award, internal grant

2022 OU 1804 Award, Acquisition of an FT-IR Spectrophotometer for Teaching and Research

2019 OU 1804 Award, Spectrometer for Education and Research in Forensic Chemistry

2019 NQPI Research Challenge Award, internal grant

2018 HTC Undergraduate Student Research Apprenticeship Fund

2017 PACE Undergraduate Student Research Fund

2017 NQPI Research Challenge Award

2016 NQPI Research Challenge Award

2015 OURC Fund

2015 HTC Undergraduate Student Research Fund

2014 Ohio University Startup Fund

Facility and in-house instruments

Sharing space with the physical chemistry division, occupying about a third of the 4000 ft^2 lab space and 6 faculty and student offices in new chemistry building east wing of 3rd floor.

• Wet lab : ~800 ft^2 equipted with benchtops, cabins, and three fume hoods, a laminar flow clean hood, water, sink, and an ultrapure water system.

• Laser lab: ~400 ft^2 equipted with hang-on power rack, storage, and light control system.

• PI and Student Offices across the hallway.

• Have access to chemistry machine shop, chemistry stockroom, physics machine shop, and electronic shop.

• Have access to NQPI and Ohio University shared equipment and facility.

In-house instruments:

• A super-resolution spectro-microscope is ready for this project. More specifically, the microscope (Nikon TiU) is equipped with four lasers (405, 473, 532, and 635 nm),  a 1.49 NA, 100x, oil-immersion objective (Nikon CFI Apo), a 20x Nikon objective, filter sets, eyepieces, and a -100 oC cooled EMCCD detector (Andor iXon 897U). The working mode can be switched between total internal reflectance fluorescence (TIRF) and Epi-fluorescence wide-field mode.

• A Raman/AFM/NSOM scanning microscope (AlphaSNOM, Witec GmbH) . This microscope incorporates confocal scanning Raman spectromicroscopy, atomic force microscopy (AFM),  and near-field scanning optical microscopy together in one microscope. The microscope has been further modified into a 4-π setup with two objectives focusing on the same plain. Several lasers have been connected to the microscope including CW lasers at 405 nm, 532 nm, and 980 nm, and a pulse laser at 532 nm. A high-resolution spectrometer (detector -100 oC) and a fast single-photon avalanche photodiode (APD) detector have been attached. A temperature-control microscope stage is equipped with this microscope. This microscope is obtained from Dr. Richardson, a recently retired colleague of the PI. This instrument is now shared in the physical chemistry division with Dr. Cimatu for teaching and research.

• An atomic force microscope (MFP 3D AFM, Asylum Research shared with Dr. Cimatu for both teaching and research).

• A differential scanning calorimeter (DSC shared with Dr. Cimatu for both teaching and research).

• A fluorometer (Horiba shared with Dr. Cimatu for teaching and research)

• MATLAB codes for data analysis of single-molecule and single-particle photoluminescence, MATLAB codes for ultrafast TA data global fitting, and PL lifetime fitting have been developed and tested in several publications.

• A Dynamic light scattering spectrometer (DynaPro).

• A VASE Ellipsometer (VASE HS-190, tunable wavelengths, also shared for teaching).

• A single-photon counting spectrofluorometer (the best time resolution is 40 ps).

• A gold sputter (Denton Vacuum) and a metal thermal evaporator.

• A Plasma cleaner (Harrick Plasma).

• Two spin coaters (MTI and Ossila).

• A solar simulator (Abet).

• A Keithley 2460 power source meter.

• A Keithley 6514 electrometer.

• A regular fluorescence microscope.

• A UV-Vis spectrometer.

• Other basic lab equipment such as balances, centrifuges, ovens, furnaces, refrigerators, safety chemical cabinets, sonicators, a probe sonicator, and a Thermo Barnstead E-Pure water purification system.

Chen Lab Equipment

Departmental Facility Center

Chemistry Building, Research and Teaching Labs