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Nguyen JH, Rana A, Dick JE. Amplifying the electrochemical footprint of <1000 molecules in a dissolving microdroplet. Analyst 2024; 149:4222-4229. [PMID: 38869006 PMCID: PMC11299638 DOI: 10.1039/d4an00504j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2024] [Accepted: 05/17/2024] [Indexed: 06/14/2024]
Abstract
The ability of analytical strategies to detect and positively identify molecules under extremely dilute conditions is important for the growth and expansion of analytical techniques and instrumentation. At present, few measurement science techniques can robustly approach the measurement of just a few thousand molecules. Here, we present an electrochemical platform for the detection and positive identification of fewer than 1000 molecules of decamethylferrocene ((Cp*)2FeII). We achieve this remarkable detection threshold by trapping (Cp*)2FeII in a 1,2-dichloroethane microdroplet, which is allowed to dissolve into an aqueous continuous phase while on a gold microelectrode (radius ∼6.25 μm). Because electrochemistry is not sensitive enough to observe the charge of less than 1000 molecules, we dissolved μM amounts hexacyanoferrate(III) in the aqueous continuous phase. The biphasic reaction between hexacyanoferrate(III) and Cp2*(Fe)II allows for a feedback loop when the microelectrode is biased sufficiently negative to reduce Cp2*(Fe)III. This feedback loop, a typical EC' catalytic mechanism, amplifies the electrochemical signal of Cp2*(Fe)II when the droplet is of small enough dimensions for feedback to occur. Our results demonstrate that clever biphasic reactions can be coupled with dissolving microdroplets to access extremely low limits of quantitation in electroanalysis.
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Affiliation(s)
- James H Nguyen
- Department of Chemistry, Purdue University, West Lafayette, IN, 47907, USA.
| | - Ashutosh Rana
- Department of Chemistry, Purdue University, West Lafayette, IN, 47907, USA.
| | - Jeffrey E Dick
- Department of Chemistry, Purdue University, West Lafayette, IN, 47907, USA.
- Elmore Family School of Electrical and Computer Engineering, Purdue University, West Lafayette, IN, 47907, USA
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Li Y, Ding J, Qin W. Enhanced Selectivity in Microdroplet-Mediated Enzyme Catalysis. J Am Chem Soc 2024. [PMID: 39073863 DOI: 10.1021/jacs.4c06171] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/30/2024]
Abstract
Natural enzymes with enhanced catalytic activity and selectivity have long been studied by tuning the microenvironment around the active site, but how to modulate the active-site electric field in a simple fashion remains challenging. Here, we demonstrate that microdroplets as a simple yet versatile reactor can enhance the electric field at the active site of an enzyme. By using horseradish peroxidase as a model, improved selectivity in microdroplet-mediated enzyme catalysis can be obtained. Quantum mechanical/molecular dynamics calculations and vibrational Stark spectroscopy reveal that the electric field at the microdroplet interface can influence the electrostatic preorganization and orientation of the enzyme to enhance its internal electric field. As a result, the free energies of the substrate and heme can be tuned by the internal electric field, thereby changing its catalytic reaction pathway for a classical substrate, 3,3',5,5'-tetramethylbenzidine, and enabling selective C-N additions for specific substrates. This finding provides a green, simple, and effective way to modulate enzyme-catalyzed reactions and holds promise for a broad spectrum of biosensing and biosynthesis applications.
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Affiliation(s)
- Yinhao Li
- CAS Key Laboratory of Coastal Environmental Processes and Ecological Remediation, Yantai Institute of Coastal Zone Research (YIC), Chinese Academy of Sciences (CAS), Shandong Key Laboratory of Coastal Environmental Processes, YICCAS, Yantai, Shandong 264003, P. R. China
- University of Chinese Academy of Sciences, Beijing 100049, P. R. China
| | - Jiawang Ding
- CAS Key Laboratory of Coastal Environmental Processes and Ecological Remediation, Yantai Institute of Coastal Zone Research (YIC), Chinese Academy of Sciences (CAS), Shandong Key Laboratory of Coastal Environmental Processes, YICCAS, Yantai, Shandong 264003, P. R. China
- University of Chinese Academy of Sciences, Beijing 100049, P. R. China
| | - Wei Qin
- CAS Key Laboratory of Coastal Environmental Processes and Ecological Remediation, Yantai Institute of Coastal Zone Research (YIC), Chinese Academy of Sciences (CAS), Shandong Key Laboratory of Coastal Environmental Processes, YICCAS, Yantai, Shandong 264003, P. R. China
- Laboratory for Marine Biology and Biotechnology, Qingdao Marine Science and Technology Center, Qingdao, Shandong 266237, P. R. China
- Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao, Shandong 266071, P. R. China
- University of Chinese Academy of Sciences, Beijing 100049, P. R. China
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Krushinski LE, Qiu L, Dick JE. Levitating Droplet Electroanalysis. Anal Chem 2024. [PMID: 38316404 DOI: 10.1021/acs.analchem.3c04123] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2024]
Abstract
Chemical reactions that occur in droplets proceed much differently compared to bulk phases. For instance, many groups have studied droplets during levitation by mass spectrometry and fluorescence to gain more detailed mechanistic insight. Such droplets maximize the probability of solution species interacting with the solution-air interface, an interface that is inherently difficult to probe electrochemically. In this Technical Note, we overcome this limitation by developing a laser-pulled dual-barrel electrode. Having two microwires sealed within the same glass capillary allows one to make two-electrode measurements. We show that the electrode can be positioned within a levitating water droplet and that the voltammetry of a redox indicator (hexacyanoferrate (II/III)) can be observed in real-time. Such foundational measurement tools are important to probe a variety of chemical reactions at complex interfaces.
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Affiliation(s)
- Lynn E Krushinski
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States
| | - Lingqi Qiu
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States
| | - Jeffrey E Dick
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States
- Elmore Family School of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana 47907, United States
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