High sensitive calixarene-based sensor for detection of dopamine by electrochemical and acoustic methods

Water-soluble pillar[5]arene sulfo-derivatives self-assemble into biocompatible nanosystems to stabilize therapeutic proteins

Pillar[5]arenes containing sulfonate fragments have been shown to form supramolecular complexes with therapeutic proteins to facilitate targeted transport with an increased duration of action and enhanced bioavailability. Regioselective synthesis was used to obtain a water-soluble pillar[5]arene containing the fluorescent label FITC and nine sulfoethoxy fragments. The pillar[5]arene formed complexes with the therapeutic proteins binase, bleomycin, and lysozyme in a 1:2 ratio as demonstrated by UV-vis and fluorescence spectroscopy. The formation of stable spherical nanosized macrocycle/binase complexes with an average particle size of 200 nm was established by dynamic light scattering and transmission electron microscopy. Flow cytometry demonstrated the ability of macrocycle/binase complexes to penetrate into tumor cells where they exhibited significant cytotoxicity towards A549 cells at 10^-5-10^-6 M while maintaining the enzymatic activity of binase.

Detection of Sub-Nanomolar Concentration of Trypsin by Thickness-Shear Mode Acoustic Biosensor and Spectrophotometry

The determination of protease activity is very important for disease diagnosis, drug development, and quality and safety assurance for dairy products. Therefore, the development of low-cost and sensitive methods for assessing protease activity is crucial. We report two approaches for monitoring protease activity: in a volume and at surface, via colorimetric and acoustic wave-based biosensors operated in the thickness-shear mode (TSM), respectively. The TSM sensor was based on a β-casein substrate immobilized on a piezoelectric quartz crystal transducer. After an enzymatic reaction with trypsin, it cleaved the surface-bound β-casein, which increased the resonant frequency of the crystal. The limit of detection (LOD) was 0.48 ± 0.08 nM. A label-free colorimetric assay for trypsin detection has also been performed using β-casein and 6-mercaptohexanol (MCH) functionalized gold nanoparticles (AuNPs/MCH-β-casein). Due to the trypsin cleavage of β-casein, the gold nanoparticles lost shelter, and MCH increased the attractive force between the modified AuNPs. Consequently, AuNPs aggregated, and the red shift of the absorption spectra was observed. Spectrophotometric assay enabled an LOD of 0.42 ± 0.03 nM. The Michaelis-Menten constant, KM, for reverse enzyme reaction has also been estimated by both methods. This value for the colorimetric assay (0.56 ± 0.10 nM) is lower in comparison with those for the TSM sensor (0.92 ± 0.44 nM). This is likely due to the better access of the trypsin to the β-casein substrate at the surface of AuNPs in comparison with those at the TSM transducer.

One novel calix[4]arene based QCM sensor for sensitive, selective and high performance-sensing of formaldehyde at room temperature

This work designs the synthesis of a novel amino morpholine schiff base functionalized calix[4]arene cage (SCC), its deposition onto Quartz Crystal Microbalance (QCM) crystal surface, and usage for the selective detecting of formaldehyde (HCHO). The SCC modified QCM sensor has been characterized by contact angle measurements and microscopy images. Initial experiments revealed that the frequency response decreased significantly which means that there was a good interaction between the SCC molecules and HCHO. The proposed sensor exhibited a linear response towards HCHO in different concentrations ranging from 1.85 to 9.25 ppm, having the high sensitivity (S) and low limit of detection (LOD) being 18.324 Hz/ppm and 0.67 ppm, respectively. Furthermore, the adsorption behavior and mechanism of HCHO onto the QCM sensor were investigated for this sensing system and the adsorption data exhibited a good correlation with the Freundlich and Langmuir-Freundlich adsorption models in terms of the regression coefficient. The QCM sensor showed outstanding selective performance to HCHO among %97 RH and some a number of interfering volatile organic compounds (VOCs) such as chloroform, dichloromethane, acetone, n-hexane, methanol, xylene, and ammonia. Thus, real-time, sensitive, selective and effective recognition of HCHO by the sensor can be explained some adsorption mechanisms such as size-fit concept, three-dimensional structures of molecules and interaction between moieties of the sensible film layer and analyte molecules such as hydrogen bonding interactions.

DNA Aptamers in the Detection of Leukemia Cells by the Thickness Shear Mode Acoustics Method

By using the thickness shear mode acoustics method (TSM) and single-molecule force spectroscopy (SMFS) we studied the interactions between DNA aptamers (sgc8c) specific to the protein tyrosine kinase 7 (PTK7), which is localized in the membranes of leukemia lymphoblastics (MOLT-4), and lymphocyte (Jurkat) cell lines, as well with PTK7-negative U266 myeloid leukemia cells. The TSM method allowed the development of a highly sensitive, label-free biosensor for the detection leukemia cells with a limit of detection of (195±20) cells/mL. SMFS approved the high selectivity of the sgc8c aptamers to the PTK7 receptors at the cell surface and allowed determining the binding probability of the aptamers to the PTK7 receptors at different cell lines.

Electrochemical detection of dopamine by a calixarene-cellulose acetate mixed Langmuir-Blodgett monolayer

The sensing performance of a Langmuir-Blodgett monolayer was significantly improved by controlling the film organization at the air-water interface. Cellulose acetate (CA) and 4-tert-butylcalix [6]arene (calix) were co-spread and formed a Langmuir film, which was efficiently transferred onto a preoxidized gold electrode, Au_ox. The modified gold electrode was applied as a fast, highly sensitive electrochemical sensing platform for the quantitative determination of a model molecule, dopamine (DA). The modified gold electrode, CA-calix/Au_ox, demonstrated better recognition and sensing ability towards dopamine as compared with electrodes modified by a single component. Under the optimized conditions, the reduction peak currents at the CA-calix/Au_ox increased linearly within the concentration range of dopamine from 5 to 100 and 100-7500 nM, and exhibited a very low limit of detection (LOD) of 2.54 nM (S/N = 3). These results suggest a simple, superior and efficient approach for the controllable rearrangement of Langmuir-Blodgett monolayers on a molecular level. The electroanalytical performance was optimized from the perspective of the electrode-electrolyte interface.

Gold Electrodes Modified with Calix[4]arene for Electrochemical Determination of Dopamine in the Presence of Selected Neurotransmitters

Here, we present an electrochemical sensor based on gold electrodes modified with calix[4]arene functionalized with carboxypiperidino groups at the upper rim. It has been demonstrated that these groups are involved in a complex formation with dopamine (DA) on the surface of gold electrodes. The supramolecular complex calix[4]arene–DA created on the gold electrode surface has been characterized electrochemically and the measuring conditions have been optimized. The presented sensor displayed a detection limit in the pM range. The DA determination was performed successfully in the presence of ascorbic acid, uric acid and selected neurotransmitters.

Carbon nanotube nanoweb-bioelectrode for highly selective dopamine sensing

A highly sensitive and selective dopamine sensor was fabricated with the unique 3D carbon nanotube nanoweb (CNT-N) electrode. The as-synthesised CNT-N was modified by oxygen plasma to graft functional groups in order to increase selective electroactive sites at the CNT sidewalls. This electrode was characterized physically and electrochemically using HRSEM, Raman, FT-IR, and cyclic voltammetry (CV). Our investigations indicated that the O(2)-plasma treated CNT-N electrode could serve as a highly sensitive biosensor for the selective sensing of dopamine (DA, 1 μM to 20 μM) in the presence of ascorbic acid (AA, 1000 μM).