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  1. Pseudomonas aeruginosa(P. aeruginosa) is a phenazine-producing pathogen recognized for its biofilm-mediated antibiotic resistance, showing up to 1000 times higher resistance compared to planktonic cells. In particular, it is shown that a phenazine called pyocyanin promotes antibiotic tolerance inP. aeruginosacultures by upregulating efflux pumps and inducing biofilm formation. Therefore, real-time study of phenazine production in response to antibiotics could offer new insights for early detection and management of the infection. Toward this goal, this work demonstrates real-time monitoring ofP. aeruginosacolony biofilms challenged by antibiotics using electrochemical sensors based on direct laser functionalization of laser induced graphene (LIG) with gold (Au) nanostructures. Specifically, two routes for functionalization of the LIG electrodes with Au-containing solutions are studied: electroless deposition and direct laser functionalization (E-Au/LIG and L-Au/LIG, respectively). While both methods show comparable sensitivity (1.276 vs 1.205μAμM−1), E-Au/LIG has bactericidal effects which make it unsuitable as a sensor material. The effect of antibiotics (gentamicin as a model drug) on the production rate of phenazines before (i.e., in planktonic phase) or after biofilm formation is studied. The sensor data confirms that theP. aeruginosabiofilms are at least 100 times more tolerant to the antibiotic compared to planktonic cells. The biosensors are developed using a scalable and facile manufacturing approach and may pave the way toward simple-to-use antibiotic susceptibility testing devices for early infection diagnosis and real-time study of antibiotic resistance evolution.

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  2. Neurotransmitters are small molecules involved in neuronal signaling and can also serve as stress biomarkers.1Their abnormal levels have been also proposed to be indicative of several neurological diseases such as Alzheimer’s disease, Parkinson’s disease, Huntington disease, among others. Hence, measuring their levels is highly important for early diagnosis, therapy, and disease prognosis. In this work, we investigate facile functionalization methods to tune and enhance sensitivity of printed graphene sensors to neurotransmitters. Sensors based on direct laser scribing and screen-printed graphene ink are studied. These printing methods offer ease of prototyping and scalable fabrication at low cost.

    The effect of functionalization of laser induced graphene (LIG) by electrodeposition and solution-based deposition of TMDs (molybdenum disulfide2and tungsten disulfide) and metal nanoparticles is studied. For different processing methods, electrochemical characteristics (such as electrochemically active surface area: ECSA and heterogenous electron transfer rate: k0) are extracted and correlated to surface chemistry and defect density obtained respectively using X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. These functionalization methods are observed to directly impact the sensitivity and limit of detection (LOD) of the graphene sensors for the studied neurotransmitters. For example, as compared to bare LIG, it is observed that electrodeposition of MoS2on LIG improves ECSA by 3 times and k0by 1.5 times.3Electrodeposition of MoS2also significantly reduces LOD of serotonin and dopamine in saliva, enabling detection of their physiologically relevant concentrations (in pM-nM range). In addition, chemical treatment of LIG sensors is carried out in the form of acetic acid treatment. Acetic acid treatment has been shown previously to improve C-C bonds improving the conductivity of LIG sensors.4In our work, in particular, acetic acid treatment leads to larger improvement of LOD of norepinephrine compared to MoS2electrodeposition.

    In addition, we investigate the effect of plasma treatment to tune the sensor response by modifying the defect density and chemistry. For example, we find that oxygen plasma treatment of screen-printed graphene ink greatly improves LOD of norepinephrine up to three orders of magnitude, which may be attributed to the increased defects and oxygen functional groups on the surface as evident by XPS measurements. Defects are known to play a key role in enhancing the sensitivity of 2D materials to surface interactions, and have been explored in tuning/enhancing the sensor sensitivity.5Building on our previous work,3we apply a custom machine learning-based data processing method to further improve that sensitivity and LOD, and also to automatically benchmark different molecule-material pairs.

    Future work includes expanding the plasma chemistry and conditions, studying the effect of precursor mixture in laser-induced solution-based functionalization, and understanding the interplay between molecule-material system. Work is also underway to improve the machine learning model by using nonlinear learning models such as neural networks to improve the sensor sensitivity, selectivity, and robustness.


    A. J. Steckl, P. Ray, (2018), doi:10.1021/acssensors.8b00726.

    Y. Lei, D. Butler, M. C. Lucking, F. Zhang, T. Xia, K. Fujisawa, T. Granzier-Nakajima, R. Cruz-Silva, M. Endo, H. Terrones, M. Terrones, A. Ebrahimi,Sci. Adv.6, 4250–4257 (2020).

    V. Kammarchedu, D. Butler, A. Ebrahimi,Anal. Chim. Acta.1232, 340447 (2022).

    H. Yoon, J. Nah, H. Kim, S. Ko, M. Sharifuzzaman, S. C. Barman, X. Xuan, J. Kim, J. Y. Park,Sensors Actuators B Chem.311, 127866 (2020).

    T. Wu, A. Alharbi, R. Kiani, D. Shahrjerdi,Adv. Mater.31, 1–12 (2019).

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    Free, publicly-accessible full text available August 28, 2024
  3. Abstract

    Pseudomonas aeruginosa(P. aeruginosa) is an opportunistic pathogen causing infections in blood and implanted devices. Traditional identification methods take more than 24 h to produce results. Molecular biology methods expedite detection, but require an advanced skill set. To address these challenges, this work demonstrates functionalization of laser‐induced graphene (LIG) for developing flexible electrochemical sensors forP. aeruginosabased on phenazines. Electrodeposition as a facile approach is used to functionalize LIG with molybdenum polysulfide (MoSx). The sensor's limit of detection (LOD), sensitivity, and specificity are determined in broth, agar, and wound simulating medium (WSM). Control experiments withEscherichia coli, which does not produce phenazines, demonstrate specificity of sensors forP. aeruginosa. The LOD for pyocyanin (PYO) and phenazine‐1‐carboxylic acid (PCA) is 0.19 × 10−6 and 1.2 × 10−6 m, respectively. Furthermore, the highly stable sensors enable real‐time monitoring ofP. aeruginosabiofilms over several days. Comparing square wave voltammetry data over time shows time‐dependent generation of phenazines. In particular, two configurations—“Normal” and “Flipped”—are studied, showing that the phenazines time dynamics vary depending on how cells interact with sensors. The reported results demonstrate the potential of the developed sensors for integration with wound dressings for early diagnosis ofP. aeruginosainfection.

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