Browsing by Subject "localized surface plasmon resonance"

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
    Achieving biosensing at attomolar concentrations of cardiac troponin T in human biofluids by developing a label-free nanoplasmonic analytical assay
    (RSC, 2017) Liyanage, Thaksila; Sangha, Andeep; Sardar, Rajesh; Chemistry and Chemical Biology, School of Science
    Acute myocardial infarction (heart attack) is the fifth leading cause of death in the United States (Dariush et al., Circulation, 2015, 131, e29–e322). This highlights the need for early, rapid, and sensitive detection of its occurrence and severity through assaying cardiac biomarkers in human fluids. Herein we report chip-based fabrication of the first label-free, nanoplasmonic biosensor to assay cardiac troponin T (cTnT) in human biofluids (plasma, serum, and urine) with high specificity. The sensing mechanism is based on the adsorption model that measures the localized surface plasmon resonance (LSPR) wavelength shift of anti-cTnT functionalized gold triangular nanoprisms (Au TNPs) induced by a change of their local dielectric environment upon binding of cTnT. We demonstrate that controlled manipulation of the sensing volume and decay length of Au TNPs together with an appropriate surface functionalization and immobilization of anti-cTnT onto TNPs allows us to achieve a limit of detection (LOD) of our cTnT assay at attomolar concentration (∼15 aM) in human plasma. This LOD is at least 50-fold more sensitive than that of other label-free techniques. Furthermore, we demonstrate excellent sensitivity of our sensors in human serum and urine. Importantly, our chip-based fabrication strategy is extremely reproducible. We believe our powerful analytical tool for detection of cTnT directly in human biofluids using this highly reproducible, label-free LSPR sensor will have great potential for early diagnosis of heart attack and thus increase patients’ survival rate.
  • Thumbnail Image
    Item
    Amplification-Free, High-Throughput Nanoplasmonic Quantification of Circulating MicroRNAs in Unprocessed Plasma Microsamples for Earlier Pancreatic Cancer Detection
    (ACS, 2023-03) Masterson, Adrianna N.; Chowdhury, Nayela N.; Yang, Yue; Yip-Schneider, Michele T.; Hati, Sumon; Gupta, Prashant; Cao, Sha; Wu, Huangbing; Schmidt, C. Max; Fishel, Melissa L.; Sardar, Rajesh; Chemistry, School of Science
    Pancreatic ductal adenocarcinoma (PDAC) is a deadly malignancy that is often detected at an advanced stage. Earlier diagnosis of PDAC is key to reducing mortality. Circulating biomarkers such as microRNAs are gaining interest, but existing technologies require large sample volumes, amplification steps, extensive biofluid processing, lack sensitivity, and are low-throughput. Here, we present an advanced nanoplasmonic sensor for the highly sensitive, amplification-free detection and quantification of microRNAs (microRNA-10b, microRNA-let7a) from unprocessed plasma microsamples. The sensor construct utilizes uniquely designed −ssDNA receptors attached to gold triangular nanoprisms, which display unique localized surface plasmon resonance (LSPR) properties, in a multiwell plate format. The formation of −ssDNA/microRNA duplex controls the nanostructure–biomolecule interfacial electronic interactions to promote the charge transfer/exciton delocalization processes and enhance the LSPR responses to achieve attomolar (10–18 M) limit of detection (LOD) in human plasma. This improve LOD allows the fabrication of a high-throughput assay in a 384-well plate format. The performance of nanoplasmonic sensors for microRNA detection was further assessed by comparing with the qRT-PCR assay of 15 PDAC patient plasma samples that shows a positive correlation between these two assays with the Pearson correlation coefficient value >0.86. Evaluation of >170 clinical samples reveals that oncogenic microRNA-10b and tumor suppressor microRNA-let7a levels can individually differentiate PDAC from chronic pancreatitis and normal controls with >94% sensitivity and >94% specificity at a 95% confidence interval (CI). Furthermore, combining both oncogenic and tumor suppressor microRNA levels significantly improves differentiation of PDAC stages I and II versus III and IV with >91% and 87% sensitivity and specificity, respectively, in comparison to the sensitivity and specificity values for individual microRNAs. Moreover, we show that the level of microRNAs varies substantially in pre- and post-surgery PDAC patients (n = 75). Taken together, this ultrasensitive nanoplasmonic sensor with excellent sensitivity and specificity is capable of assaying multiple biomarkers simultaneously and may facilitate early detection of PDAC to improve patient care.
  • Thumbnail Image
    Item
    Designing of Gold Nanoprism-Based Reversible and Ultra-sensitive Molecular Sensors
    (Office of the Vice Chancellor for Research, 2013-04-05) Joshi, Gayatri K.; Smith, Kimberly A.
    Photoswitchable molecules have attracted a great deal of attention over the past few years in designing molecular machines. Among photoswitchable molecules, azobenzene is widely studied due to its transcis photoisomeration, which produces a simple structure and spectra, and is photo and electrochemically active. The localized surface plasmon resonance (LSPR) properties of the metal nanostructures in conjunction with the photswitching properties of the azobenzene molecules allow the nanoscale environment to be more controlled and to ultimately improve the sensing abilities of the metallic nanostructures. We have developed a method of constructing a self-assembled monolayer (SAM) of azobenzene-containing alkanethiol molecules on the surface of chemically synthesized gold nanoprisms as molecular sensor. The reversible photoswiching properties of azobenzene were studied by monitoring the LSPR peak shift of gold nanoprisms by absorption spectroscopy. It was found that the substratebound gold nanoprisms functionalized with azobenzene alkanethiol molecules resulted in a ~30 nm LSPR peak red shift. The photoswitching behavior of the azobenzene molecules attached to the prisms was monitored after cycling exposure to UV and visible light. A ~12 nm LSPR blue shift was observed as the light exposure was switched from visible to UV light due to the trans to cis isomeration of the azobenze. The LSPR peak shift was found to be reversible as the light source was switched back and forth several times from UV to visible light. The reversible photoswitching of azobenzene-functionalized gold nanoprisms demonstrates their potential as ultra-sensitive molecular sensors for a broad range of applications from nanoelectrochemical systems to medicine.
  • Thumbnail Image
    Item
    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.