Research

Research interest:

Biosensors, Electrochemistry, Nanotechnology, Nanostructured Microelectrodes, Wearables, Cancer, Pathogens & COVID-19

Our aim is to develop ultrasensitive sensors applicable to the diagnosis of cancer, pathogens, and other diseases, and development of wearables technologies for continuous monitoring of diseases. 

An ultrasensitive and simple cost-effective method for detecting and quantifying biomarkers is essential for early diagnosis of diseases. If a disease is detectable in the early stage its treatment would be easier.

1) Detection of protein biomarkers

2) Detection of nucleic acids

3) Detection of pathogens including COVID-19

4) Detection of circulating nucleic acids (liquid biopsy)

5) Detection of small molecules

6) Reagentless assay

7) Wearables

Reagentless assay based on molecular pendulum for continuous and real-time disease monitoring.

The development of reagentless sensors that can detect molecular analytes in biological fluids could enable a broad range of applications in personalized health monitoring. However, only a limited set of molecular inputs can currently be detected using reagentless sensors. Here, we report a sensing mechanism that is compatible with the analysis of proteins that are important physiological markers of stress, allergy, cardiovascular health, inflammation and cancer. The sensing method is based on the motion of an inverted molecular pendulum that exhibits field-induced transport modulated by the presence of a bound analyte. We measure the sensor’s electric field-mediated transport using the electron-transfer kinetics of an attached reporter molecule. Using time-resolved electrochemical measurements that enable unidirectional motion of our sensor, the presence of an analyte bound to our sensor complex can be tracked continuously in real time. We show that this sensing approach is compatible with making measurements in blood, saliva, urine, tears and sweat and that the sensors can collect data in situ in living animals.

1) Jagotamoy Das, Surath Gomis, Jenise Chen, Hanie Yousefi, Sharif Ahmed, Alam Mahmud, Wendi Zhou, Edward H. Sargent, Shana O. Kelley, Reagentless Biomolecular Analysis Using a Molecular Pendulum, Nature Chemistry, 13, 428–434 (2021).

2) Hanie Yousefi, Alam Mahmud, Dingran Chang, Jagotamoy Das, Surath Gomis, Jenise Chen, Hansen Wang, Terek Been, Lily Yip, Eric Coomes, Zhijie Li, Samira Mubareka, Allison McGeer, Natasha Christie, Scott Gray-Owen, Alan Cochrane, James M. Rini, Edward H. Sargent, Shana O. Kelley, Detection of SARS-CoV-2 Viral Particles using Direct, Reagent-Free Electrochemical Sensing, Journal of the American Chemical Society, 143, 4, 1722–1727 (2021).

3) Amanda Clifford, Jagotamoy Das, Hanie Yousefi, Alam Mahmud, Shana O. Kelley, Reagentless Strategies for Biomolecular Analysis and Continuous Physiological Monitoring, Journal of the American Chemical Society, 143, 5281–5294 (2021).

4) H. Zargartalebi, H. Yousefi, C. D. Flynn, S. Gomis, J. Das, T. L. Young, E. Chien, S. Mubareka, A. McGeer, H. Wang, E. H. Sargent, A. S. Nezhad, and S. O. Kelley, “Capillary-Assisted Molecular Pendulum Bioanalysis”, J. Am. Chem. Soc., 144, 40, 18338-18349 (2022). 

Pathogen detection.

1) Hanie Yousefi, Alam Mahmud, Dingran Chang, Jagotamoy Das, Surath Gomis, Jenise Chen,  Hansen Wang, Terek Been, Lily Yip, Eric Coomes, Zhijie Li, Samira Mubareka, Allison McGeer, Natasha Christie, Scott Gray-Owen, Alan Cochrane, James M. Rini, Edward H. Sargent, Shana O. Kelley, Detection of SARS-CoV-2 Viral Particles using Direct, Reagent-Free Electrochemical Sensing, Journal of the American Chemical Society, 143, 4, 1722–1727  (2021).

2) Thamina Acter, Nizam Uddin, Jagotamoy Das, AfrozaAkhter, Tasrina Rabia Choudhury, Sunghwan Kim, "Evolution of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) as coronavirus disease 2019 (COVID-19) pandemic: A global health emergency" Science of The Total Environment, 730, 138996 (2020)

3) Jagotamoy Das, Kristin B. Cederquist, Alexendre A. Zaragoza, Paul Lee, Edward H. Sargent, and Shana O. Kelley, "An Ultrasensitve Universal Detector Based on Neutralizer Displacement," Nature Chemistry, 4, 642-648. (2012)

4) Brian Lam, Jagotamoy Das, Richard D. Holmes, Ludovic Live, Andrew Sage, Edward H. Sargent, and  Shana O. Kelley, "Solution-Based Circuits Enable Rapid and Multiplexed Pathogen Detection," Nature Communications, 4:2001, 1-8 (2013)

5) Justin D. Besant, Jagotamoy Das, Edward H. Sargent, and Shana O. Kelley, "Proximal Bacterial Lysis and Detection in Nanoliter Wells Using Electrochemistry," ACS Nano, 7 (9), 8183–8189. (2013)

Jagotamoy Das and Shana O. Kelley, "Tuningthe Bacterial Detection Sensitivity of Nanostructured Microelectrodes," Analytical Chemistry, 85, 7333-73338 (2013)

6) Wenhan Liu, Jagotamoy Das, Carine Nemr, Edam Mepham, Edward H. Sargent, and Shana O. Kelley,"A Fully-Integrated Testing Device for PCR-FreeViral Nucleic Acid Detection in Whole Blood,” Lab Chip, 18, 1928-1935 (2018)

7) Jagotamoy Das, Kristin B. Cederquist, Alexendre A. Zaragoza, Paul Lee, Edward H. Sargent, and Shana O. Kelley, "An Ultrasensitve Universal Detector Based on Neutralizer Displacement," Nature Chemistry, 4, 642-648. (2012).  

Detection of circulating nucleic acids (liquid biopsy).

1) Jagotamoy Das, Ivaylo Ivanov, Laura Montermini, Janusz Rak, Edward H. Sargent, and Shana O. Kelley, "An electrochemical clamp assay for direct, rapid analysis of circulating nucleic acids in serum," Nature Chemistry, 7, 569 - 575 (2015)

2) agotamoy Das, Ivaylo Ivanov, Edward H. Sargent, and Shana O. Kelley, "DNA Clutch Probes for Circulating Tumor DNA Analysis," Journal of the American Chemical Society, 138 (34), 11009-11016 (2016)

3) Jagotamoy Das, Ivaylo Ivanov, Tina S. Safei, Edward H. Sargent, and Shana O. Kelley, "Combinatorial Probes for High-Throughput Electrochemical Analysis of Circulating Nucleic Acids in Patient Samples," Angew. Chemie. Int. Ed., 57, 3711- 3716 (2018)

4) Jagotamoy Das and Shana O. Kelley, "High-Performance Nucleic Acid Sensors for Liquid Biopsy Applications," Angew. Chemie. Int. Ed., 59 (7), 2554-2564 (2020)

Ultrasensitive readout of CA-125 in Serum and whole blood using nanostructured microelectrodes on electronic chips.

Multiplexed assays that can measure protein biomarkers and internal standards are highly desirable given the potential to reduce false positives and negatives. We report here the use of a chip-based platform that achieves multiplexed immunosensing of the ovarian cancer biomarker CA-125 without the need for covalent labeling or sandwich complexes. The sensor chips allow the straightforward comparison of detectors of different sizes, and we used this feature to scan the microscale size regime for the best sensor size and optimize the limit of detection exhibited down to 0.1 U/mL. The assay has a straightforward design, with readout being performed in a single step involving the introduction of a noncovalently attached redox reporter group. The detection system reported exhibits excellent specificity, with analysis of a specific cancer biomarker, CA-125, performed in human serum and whole blood. The multiplexing of the system allows the analysis of the biomarker to be performed in parallel with an abundant serum protein for internal calibration.

References:

1) Das, J.; Kelley, S. O.  Anal. Chem., 2011, 83(4), 1167–1172. 

Ultrasensitive detection of proteins and nucleic acids using nanocatalysts.

We developed a novel nanocatalyst-based electrochemical assay with an ultrahigh sensitivity without using DNA or enzymatic amplification. The Ultrasensitive detection has been achieved by signal amplification combined with noise reduction: the signal is amplified both by the catalytic reduction of p-nitrophenol to p-aminophenol by gold-nanocatalyst labels and by the chemical reduction of p-quinone imine to p-aminophenol by NaBH4; the noise is reduced by employing an indium tin oxide (ITO) electrode modified with partially ferrocenyl-tethered dendrimer (Fc-D) and a hydrophilic immunosensing layer.

For the preparation of a sandwich-type heterogeneous electrochemical immunosensor, an IgG layer was formed on an ITO electrode. First, Fc-D was immobilized to the ITO electrode by covalent bonding between dendrimer amines and carboxylic acids of a phosphonate self-assembled monolayer. Some of the unreacted amines of Fc-D were modified with biotin groups to allow the specific binding of streptavidin. Afterwards, biotinylated antibodies were immobilized to the streptavidin-modified ITO electrode. An IgG-nanocatalyst conjugate was prepared via direct adsorption of IgG on 10-nm gold nanoparticles. Mouse IgG or prostate specific antigen was chosen as a target protein. The IgG-nanocatalyst conjugate and the immunosensing layer sandwich the target protein. The gold-nanocatalyst label generates p-aminophenol by catalytic reduction. This reaction is very fast, and its kinetic values (kcat and kcat/KM) are large and not decreased significantly even after IgG conjugation to gold nanocatalyst. Thus generated AP molecules are electrochemically oxidized to QI via an electron mediation of ferrocene. The oxidized QI is then reduced back to AP by NaBH4. The wide range of concentrations (1 fg/mL to 10 mg/mL) can be detected in a single assay format and we obtained a detection limit of 1 fg/mL for both analytes.

We further explored the catalytic property of gold nanoparticles to detect nucleic acid.

References:

1) Das, J.; Aziz, M. A.; Yang, H. J. Am. Chem. Soc., 2006, 128 (50), 16022-16023.

2) Selvaraju, T.; Das, J.; Han, S.; W.; Yang, H. Biosens. Bioelectron., 2008, 23 (7), 932-938.

3) Salvaraju, T.; Das, J.; Jo, K., Kwon, K.; Huh, C.-H., Kim, T. K.; Yang, H.  Langmuir, 2008, 24 (17), 9883-9888.

Ultrasensitive detection of proteins using redox-cycling by hydrazine.

 Signal amplification and noise reduction are crucial for obtaining low detection limits in biosensors. Here, we developed an electrochemical immunosensor in which the signal amplification is achieved using p-aminophenol (AP) redox cycling by hydrazine, and the noise level is reduced by implementing a low background current. The redox cycling is obtained in a simple one-electrode, one-enzyme format. In a sandwich-type heterogeneous immunosensor for mouse IgG, an alkaline phosphatase label converts p-aminophenyl phosphate into AP for 10 min. This generated AP is electrooxidized at an indium tin oxide (ITO) electrode modified with a partially ferrocenyl-tethered dendrimer (Fc-D). The oxidized product, p-quinone imine (QI), is reduced back to AP by hydrazine, and then AP is electrooxidized again to QI, resulting in redox cycling. Moreover, hydrazine protects AP from oxidation by air, enabling long incubation times. The small amount of ferrocene in a 0.5% Fc-D-modified ITO electrode, where 0.5% represents the ratio of ferrocene groups to dendrimer amines, results in a low background current, and this electrode exhibits high electron-mediating activity for AP oxidation. Moreover, there is insignificant hydrazine electrooxidation on this electrode, which also results in a low background current. The detection limit of the immunosensor using a 0.5% Fc-D-modified electrode is 2 orders of magnitude lower than that of a 20% Fc-D-modified electrode (10 pg/mL vs 1 ng/mL). Furthermore, the presence of hydrazine reduces the detection limit by an additional 2 orders of magnitude (100 fg/mL vs 10 pg/mL). These results indicate that the occurrence of redox cycling combined with a low background current yields an electrochemical immunosensor with a very low detection limit (100 fg/mL). Mouse IgG could be detected at concentrations ranging from 100 fg/mL to 100 μg/mL (i.e., 9 orders of magnitude) in a single assay.

References:

1) Das, J.; Jo, K., Lee, J. W.; Yang, H. Anal. Chem., 2007, 79 (7), 2790-2796. 

 Ultrasensitive detection of nucleic acids using enhanced electrocatalytic activity of metallic nanoparticles.

Hydrazine electrooxidation readily occurs on bare gold nanoparticle, whereas it does not on DNA-conjugated gold nanoparticle. Thus, when DNA-conjugated gold nanoparticles are used as electrocatalytic labels in electrochemical DNA detection, anodic current of hydrazine is not easily observed within potential window because of the high overpotential caused by the slow electron-transfer kinetics on DNA-conjugated gold nanoparticle as well as the slow electron tunneling between gold nanoparticle and ITO electrode. NaBH4 treatment significantly enhances the electrocatalytic activity of DNA-conjugated gold nanoparticles. Such treatment allows extensive adsorption/absorption of hydrogen species on/into the gold nanoparticles, thereby forming an activated state which remains even after the hydrogen species have been removed. The adsorbed/absorbed hydrogen species are oxidized in air (or in solution), and the hydrogen-induced activated state slowly returns to the original, hydrogen-free state. This enhancement substantially decreases the overpotential caused by the slow electron-transfer kinetics, and anodic current of hydrazine can be measured within potential window if the distance between gold nanoparticle and ITO electrode is not too large. The enhancement with NaBH4 treatment allows high signal current, and the low intrinsic electrocatalytic activity of ITO electrodes allows low background current. The nonspecific binding of the DNA-conjugated gold nanoparticles are minimized by using ITO electrodes modified with carboxylated dendrimer. The high signal-to-background ratio enables us to detect 1 fM target DNA without target amplification or enzymatic signal amplification. The ultrasensitive detection using versatile gold nanoparticle and simple chemical treatment is practically appealing.

We also reported an ultrasensitive DNA sensor using the rapid enhancement of electrocatalytic activity of DNA-conjugated Pd nanoparticles; the rapid enhancement results from the fast catalytic hydrolysis of NaBH4 on Pd nanoparticles and subsequent fast hydrogen sorption into Pd nanoparticles.

References:

1) Das, J.; Patra, S.; Yang, H. Chem. Commun., 2008, 4451–4453. 

2) Das, J.; Yang, H. J. Phys. Chem. C, 2009, 113 (15), 6093-6099.

3) Das, J.; Kim, H.; Jo, K.; Park K. H.; Jon, S.; Lee, K.; Yang, H. Chem. Commun., 2009, 6394–6396.


Small molecule detection.

1) Jagotamoy Das, Kristin B. Cederquist, Alexendre A. Zaragoza, Paul Lee, Edward H. Sargent, and Shana O. Kelley, "An Ultrasensitve Universal Detector Based on Neutralizer Displacement," Nature Chemistry, 4, 642-648. (2012).

2) Hyun Ju Kang, Srikanta Patra, Jagotamoy Das, Md. Abdul Aziz, Jinkyung Jo, and Haesik Yang, "Effect of Aging on the Electrocatalytic Activity of Gold Nanoparticles," Electrochemistry Communications, 12, 1245–1248 (2010).

3) Jagotamoy Das, Srikanta Patra, and Haesik Yang, "Enhancement of the Electrocatalytic Activity of Gold Nanoparticles via NaBH4 Treatment," Chemical Communications, (37), 4451-4453 (2008). 

4) Jinkyo Jeong, Jagotamoy Das, Moonjung Choi, Jinkyung Jo, Md. Abdul Aziz and Haesik Yang, “Arsenic(III) Detection UsingElectrochemical-Chemical-Chemical Redox Cycling at Bare Indium‒Tin Oxide Electrodes,” Analyst, 139 (22), 5814-5818 (2014)