Browsing by Author "Johnson, Merrell"

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    Highly specific plasmonic biosensors for ultrasensitive microRNA detection in plasma from pancreatic cancer patients
    (American Chemical Society, 2014-12-10) Joshi, Gayatri K.; Deitz-McElyea, Samantha; Johnson, Merrell; Mali, Sonali; Korc, Murray; Sardar, Rajesh; Department of Chemistry & Chemical Biology, School of Science
    MicroRNAs (miRs) are small noncoding RNAs that regulate mRNA stability and/or translation. Because of their release into the circulation and their remarkable stability, miR levels in plasma and other biological fluids can serve as diagnostic and prognostic disease biomarkers. However, quantifying miRs in the circulation is challenging due to issues with sensitivity and specificity. This Letter describes for the first time the design and characterization of a regenerative, solid-state localized surface plasmon resonance (LSPR) sensor based on highly sensitive nanostructures (gold nanoprisms) that obviates the need for labels or amplification of the miRs. Our direct hybridization approach has enabled the detection of subfemtomolar concentration of miR-X (X = 21 and 10b) in human plasma in pancreatic cancer patients. Our LSPR-based measurements showed that the miR levels measured directly in patient plasma were at least 2-fold higher than following RNA extraction and quantification by reverse transcriptase-polymerase chain reaction. Through LSPR-based measurements we have shown nearly 4-fold higher concentrations of miR-10b than miR-21 in plasma of pancreatic cancer patients. We propose that our highly sensitive and selective detection approach for assaying miRs in plasma can be applied to many cancer types and disease states and should allow a rational approach for testing the utility of miRs as markers for early disease diagnosis and prognosis, which could allow for the design of effective individualized therapeutic approaches.
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    A Novel Liquid Biopsy-Based Approach for Highly Specific Cancer Diagnostics: Mitigating False Responses in Assaying Patient Plasma-Derived Circulating microRNAs through Combined SERS and Plasmon-Enhanced Fluorescence Analyses
    (RSC, 2020) Masterson, Adrianna N.; Liyanage, Thakshila; Berman, Claire; Kaimakliotis, Hristos; Johnson, Merrell; Sardar, Rajesh; Chemistry and Chemical Biology, School of Science
    Studies have shown that microRNAs, which are small noncoding RNAs, hold tremendous promise as next-generation circulating biomarkers for early cancer detection via liquid biopsies. A novel, solid-state nanoplasmonic sensor capable of assaying circulating microRNAs through a combined surface-enhanced Raman scattering (SERS) and plasmon-enhanced fluorescence (PEF) approach has been developed. Here, the unique localized surface plasmon resonance properties of chemically-synthesized gold triangular nanoprisms (Au TNPs) are utilized to create large SERS and PEF enhancements. With careful modification to the surface of Au TNPs, this sensing approach is capable of quantifying circulating microRNAs at femtogram/microliter concentrations. Uniquely, the multimodal analytical methods mitigate both false positive and false negative responses and demonstrate the high stability of our sensors within bodily fluids. As a proof of concept, microRNA-10b and microRNA-96 were directly assayed from the plasma of six bladder cancer patients. Results show potential for a highly specific liquid biopsy method that could be used in point-of-care clinical diagnostics to increase early cancer detection or any other diseases including SARS-CoV-2 in which RNAs can be used as biomarkers.
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    Reversible Tuning of the Plasmoelectric Effect in Noble Metal Nanostructures Through Manipulation of Organic Ligand Energy Levels
    (ACS, 2019-11) Liyanage, Thakshila; Nagaraju, Malpuri; Johnson, Merrell; Muhoberac, Barry B.; Sardar, Rajesh; Chemistry and Chemical Biology, School of Science
    Ligand-controlled tuning of localized surface plasmon resonance (LSPR) properties of noble metal nanostructures is fundamentally important for various optoelectronic applications such as photocatalysis, photovoltaics, and sensing. Here we demonstrate that the free carrier concentration of gold triangular nanoprisms (Au TNPs) can be tuned up to 12% upon functionalization of their surface with different para-substituted thiophenolate (X–Ph–S−) ligands. We achieve this unprecedentedly large optical response (plasmoelectric effect) in TNPs through the selective manipulation of electronic processes at the Au–thiolate interface. Interestingly, thiophenolates with electron withdrawing (donating) groups (X) produce λLSPR blue (red) shifts with broadening (narrowing) of localized surface plasmon resonance peak (λLSPR) line widths. Surprisingly, these experimental results are opposite to a straightforward application of the Drude model. Utilizing density functional theory calculations, we develop here a frontier molecular orbital approach of Au-thiophenolate interactions in the solid-state to delineate the observed spectral response. Importantly, all the spectroscopic properties are fully reversible by exchanging thiophenolates containing electron withdrawing groups with thiophenolates having electron donating groups, and vice versa. On the basis of the experimental data and calculations, we propose that the delocalization of electrons wave function controls the free carrier concentration of Au and thus the LSPR properties rather than simple electronic properties (inductive and/or resonance effects) of thiophenolates. This is further supported by the experimentally determined work functions, which are tunable over 1.9 eV in the X–Ph–S–passivated Au TNPs. We believe that our unexpected finding has great potential to guide in developing unique noble metal nanostructure–organic ligand hybrid nanoconjugates, which could allow us to bypass the complications associated with off-resonance LSPR activation of noble metal-doped semiconductor nanocrystals for various surface plasmon-driven applications.