Electrochemical and X-ray Photoelectron Spectroscopy Surface Characterization of Interchain-Driven Self-Assembled Monolayer (SAM) Reorganization

Herein, we report a combined strategy encompassing electrochemical and X-ray photoelectron spectroscopy (XPS) experiments to investigate self-assembled monolayer (SAM) conformational reorganization onto an electrode surface due to the application of an electrical field. In particular, 3-mercaptopriopionic acid SAM (3MPA SAM) modified gold electrodes are activated with a 1-ethyl-3- (3-dimethylaminopropyl)carbodiimide (EDC) and N-hydroxysulfosuccinimide (NHSS) (EDC-NHSS) mixture by shortening the activation time, from 2 h to 15/20 min, labelled as Protocol-A, -B and -C, respectively. This step, later followed by a deactivation process with ethanolamine (EA), plays a key role in the reaction yields (formation of N-(2-hydroxyethyl)-3-mercaptopropanamide, NMPA) but also in the conformational rearrangement observed during the application of the electrical field. This study aims at explaining the high performance (i.e., single-molecule detection at a large electrode interface) of bioelectronic devices, where the 3MPA-based SAM structure is pivotal in achieving extremely high sensing performance levels due to its interchain interaction. Cyclic voltammetry (CV) experiments performed in K4Fe(CN)6:K3Fe(CN)6 for 3MPA SAMs that are activated/deactivated show similar trends of anodic peak current (IA) over time, mainly related to the presence of interchain hydrogen bonds, driving the conformational rearrangements (tightening of SAMs structure) while applying an electrical field. In addition, XPS analysis allows correlation of the deactivation yield with electrochemical data (conformational rearrangements), identifying the best protocol in terms of high reaction yield, mainly related to the shorter reaction time, and not triggering any side reactions. Finally, Protocol-C’s SAM surface coverage, determined by CV in H2SO4 and differential pulse voltammetry (DPV) in NaOH, was 1.29 * 1013 molecules cm2, being similar to the bioreceptor surface coverage in single-molecule detection at a large electrode interface

Chitosan Glutamate-Coated Niosomes: a proposal for Nose-to-Brain delivery

The aim of this in vitro study is to prepare and characterize drug free and pentamidine loaded chitosan glutamate coated niosomes for intranasal drug delivery to reach the brain through intranasal delivery. Mucoadhesive properties and stability testing in various environments were evaluated to examine the potential of these formulations to be effective drug delivery vehicles for intranasal delivery to the brain. Samples were prepared using thin film hydration method. Changes in size and ζ-potential of coated and uncoated niosomes with and without loading of pentamidine in various conditions were assessed by dynamic light scattering (DLS), while size and morphology were also studied by atomic force microscopy (AFM). Bilayer properties and mucoadhesive behavior were investigated by fluorescence studies and DLS analyses, respectively. Changes in vesicle size and ζ-potential values were shown after addition of chitosan glutamate to niosomes, and when in contact with mucin solution. In particular, interactions with mucin were observed in both drug free and pentamidine loaded niosomes regardless of the presence of the coating. The characteristics of the proposed systems, such as pentamidine entrapment and mucin interaction, show promising results to deliver pentamidine or other possible drugs to the brain via nasal administration

Enzyme based field effect transistor: State‐of‐the‐art and future perspectives

Abstract The review discloses the historical and technological evolution of enzyme‐based field‐effect transistors (EnFETs) underlying the importance of gate electrode modification toward the implementation of novel FETs configurations such as extended‐gate FET (EG‐FETs) or EG organic FETs (EG‐OFETs). The working principle of the EnFETs as postulated by Bergveld in 1970, who defined the EnFET as an ion‐selective FET (ISFET) modified with enzyme‐membrane, is also discussed considering the analytical equations related to the EnFET output response. For each category, namely EnFETs, EG‐FETs, and EG‐OFETs, we reviewed the key devices’ configurations that addressed the research in this field in the last 40 years with particular attention to the analytical figures of merit

Enzyme based amperometric wide field biosensors: Is single-molecule detection possible?

This review discloses the technological advances involving enzyme-based amperometric biosensors engaging challenging limits of detection as low as a single molecule. At first, we summarise the most recent findings concerning electrode modification toward the enhancement of the enzyme loading accomplished mainly through the deposition of nanomaterials. The increase of the electron transfer (ET) rate is mostly based on the enzyme site-specific immobilization through the analysis of the enzyme structure/sequence and protein bioengineering is overviewed. However, both approaches are not appropriate to develop enzyme-based amperometric biosensors able to reach reliable analytical detections below micro-/nano-molar. The last part is devoted to single-molecule electrochemistry that has been widely exploited as a near-field approach in the last decades as a proof-of-concept for the detection of single ET events. Organic electrochemical transistors operated as Faradaic current amplifiers do not detect below micro-/nano-molar. We here propose an alternative approach based on the combination of an electrochemical cell with a bipolar junction transistor in the extended base configuration, drawing some conclusions and future perspectives on the detection of single ET events at a large electrode for the development of Point-of-Care devices

Electropolymerized molecularly imprinted polypyrrole film for dimethoate sensing: investigation on template removal after the imprinting process

The development of ultrasensitive analytical detection methods for organophosphorus pesticides such as dimethoate (DMT) plays a key role in healthy food production. DMT is an inhibitor of acetylcholinesterase (AChE), which can lead to the accumulation of acetylcholine and result in symptoms related to the autonomous and central nervous systems. Herein, we report the first spectroscopic and electrochemical study on template removal after an imprinting process from a polypyrrole-based molecularly imprinted polymer (PPy-MIP) film for the detection of DMT. Several template removal procedures were tested and evaluated using X-ray photoelectron spectroscopy. The most effective procedure was achieved in 100 mM NaOH. The proposed DMT PPy-MIP sensor exhibits a limit of detection of (8 +/- 2) x 10(-12) M

Single Molecule with a Large Transistor – SiMoT cytokine IL-6 Detection Benchmarked against a Chemiluminescent Ultrasensitive Immunoassay Array

Early diagnosis and efficient treatments of oncological, neurological, inflammatory, and infectious diseases rely more and more on ultrasensitive detection of protein markers; the ultimate limit is a reliable immunoassay capable of single-protein detection. Among protein biomarkers, cytokines play a key role in clinical diagnosis as they are involved in developing many complex diseases and disorders, such as chronic inflammatory diseases including metabolic syndrome, neurodegenerative diseases, and cardiovascular diseases, along with autoimmune diseases and cancer. Herein, the improvement of a Single Molecule with Transistor (SiMoT) is reported based on an electrolyte-gated organic field-effect transistor applied for the detection of cytokine IL-6 in blood serum, reaching a limit-of-detection (LOD) of 1 ± 1 protein in a sample of 0.1 mL. The analytical performance levels are benchmarked against the Simoa Planar Array SP-X technology, a benchtop chemiluminescent array. After comprehensive optimization, Simoa SP-X by using a multivariate experimental design approach exhibits a LOD 103 higher than SiMoT. The proposed SiMoT electronic assay is label-free, fast (30 min), and selective, paving the way for an ultra-sensitive point-of-care immunoassay platform enabling pre-symptomatic disease diagnosis

Water-Based Conductive Ink Formulations for Enzyme-Based Wearable Biosensors

Herein, this work reports the first example of second-generation wearable biosensor arrays based on a printed electrode technology involving a water-based graphite ink, for the simultaneous detection of l-lactate and d-glucose. The water-based graphite ink is deposited onto a flexible polyethylene terephthalate sheet, namely stencil-printed graphite (SPG) electrodes, and further modified with [Os(bpy)2(Cl)(PVI)10] as an osmium redox polymer to shuttle the electrons from the redox center of lactate oxidase from Aerococcus viridans (LOx) and gluocose oxidase from Aspergillus niger (GOx). The proposed biosensor array exhibits a limit of detection as low as (9.0 ± 1.0) × 10−6 m for LOx/SPG-[Os(bpy)2(Cl)(PVI)10] and (3.0 ± 0.5) × 10−6 m for GOx/SPG-[Os(bpy)2(Cl)(PVI)10], a sensitivity as high as 1.32 uA mm−1 for LOx/SPG-[Os(bpy)2(Cl)(PVI)10] and 28.4 uA mm−1 for GOx/SPG-[Os(bpy)2(Cl)(PVI)10]. The technology is also selective when tested in buffer and artificial sweat and is endowed with an operational/storage stability of ≈80% of the initial signal retained after 20 days. Finally, the proposed array is integrated in a wristband and successfully tested for the continuous monitoring of l-lactate and d-glucose in a healthy volunteer during daily activity. This is foreseen as a real-time wearable device for sport-medicine and healthcare applications

Water‐Based Conductive Ink Formulations for Enzyme‐Based Wearable Biosensors

Abstract Herein, this work reports the first example of second‐generation wearable biosensor arrays based on a printed electrode technology involving a water‐based graphite ink, for the simultaneous detection of l‐lactate and d‐glucose. The water‐based graphite ink is deposited onto a flexible polyethylene terephthalate sheet, namely stencil‐printed graphite (SPG) electrodes, and further modified with [Os(bpy)2(Cl)(PVI)10] as an osmium redox polymer to shuttle the electrons from the redox center of lactate oxidase from Aerococcus viridans (LOx) and gluocose oxidase from Aspergillus niger (GOx). The proposed biosensor array exhibits a limit of detection as low as (9.0 ± 1.0) × 10−6 m for LOx/SPG‐[Os(bpy)2(Cl)(PVI)10] and (3.0 ± 0.5) × 10−6 m for GOx/SPG‐[Os(bpy)2(Cl)(PVI)10], a sensitivity as high as 1.32 μA mm−1 for LOx/SPG‐[Os(bpy)2(Cl)(PVI)10] and 28.4 μA mm−1 for GOx/SPG‐[Os(bpy)2(Cl)(PVI)10]. The technology is also selective when tested in buffer and artificial sweat and is endowed with an operational/storage stability of ≈80% of the initial signal retained after 20 days. Finally, the proposed array is integrated in a wristband and successfully tested for the continuous monitoring of l‐lactate and d‐glucose in a healthy volunteer during daily activity. This is foreseen as a real‐time wearable device for sport‐medicine and healthcare applications

Satureja montana L. essential oils. Chemical profiles/phytochemical screening, antimicrobial activity and o/w nanoemulsion formulations

Chemical fingerprints of four different Satureja montana L. essential oils (SEOs) were assayed by an untargeted metabolomics approach based on Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometry (MS) coupled with either electrospray ionization or atmospheric pressure chemical ionization ion sources. Analysis and relative quantification of the non-polar volatile fraction were conducted by gas chromatography (GC) coupled to MS. FT-ICR MS confirmed significant differences in the polar metabolite composition, while GC-MS analyses confirmed slight fluctuations in the relative amount of major terpenes and terpenoids, known to play a key role in antimicrobial mechanisms. Oil in eater (O/W) nanoemulsions (NEs) composed by SEOs and Tween 20 or Tween 80 were prepared and analyzed in terms of hydrodynamic diameter, ζ-potential and polydispersity index. The results confirm the formation of stable NEs homogeneous in size. Minimum inhibitory and minimum bactericidal concentrations of SEOs were determined towards Gram-positive (Listeria monocytogenes, Staphylococcus aureus, Staphylococcus haemolyticus) and Gram-negative clinical isolates (Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Serratia marcescens). Commercial SEO showed strongest antibacterial activity, while SEO 3 was found to be the most active among the lab made extractions. MIC and MBC values ranged from 0.39 to 6.25 mg·mL-1. Furthermore, a SEO structured in NEs formulation was able to preserve and improve antimicrobial activity