Vesicular Sensor Research Articles

Tailored functional polymeric vesicles as smart nanostructured materials for aqueous monitoring of transition metal cations

In this study, we report the newly engineered functional polymeric vesicles as the robust nanostructured materials for the recognition and quantification of transition metal cations i.e. Hg(II) and Cr(III) as the naked eye recognition architectures in aqueous solution. The as prepared visual detector was synthesized by the combination of a hyperbranched poly(3-ethyl-3-oxetanemethanol)-star-poly(ethylene oxide) (HBPO-star-PEO, HSP) functionalized with rhodamine-2-amino-5-bromopyrimidine based chemosensor (RBP). The nanostructured vesicular sensor was regarded as HSP-RBP sensor. The naked eye detection owes from the spriolactam ring opening of the rhodamine based sensor (RBP) which was grafted onto the multiarm hyperbranched amphiphilic polymer. This newly synthesized sensor can facilely self-assemble into vesicles with enriched RBP groups on the outer surface of amphiphilic polymer. As a result of the introduction of these analytes (Hg2+/Cr3+) the structural changes of RBP takes place and a transition in color change from colorless solution to pink colored solution takes place. This transition of color can clearly be seen with bare eye. Therefore, the term visual detection can be coined for the vesicular sensor. Furthermore, the limit of detection for Hg2+ and Cr3+ was calculated as low as 1.2 and 2.9 μM respectively. The striking feature of the newly prepared sensor, is its extraordinary ability for the recognition and quantification of Hg2+/Cr3+ with outstanding selectivity in raw water samples.

EGTA Can Inhibit Vesicular Release in the Nanodomain of Single Ca2+ Channels.

The exogenous Ca2+ chelator EGTA (ethylene glycol tetraacetic acid) has been widely used to probe the coupling distance between Ca2+ channels and vesicular Ca2+ sensors for neurotransmitter release. Because of its slow forward rate for binding, EGTA is thought to not capture calcium ions in very proximity to a channel, whereas it does capture calcium ions at the remote distance. However, in this study, our reaction diffusion simulations (RDSs) of Ca2+ combined with a release calculation using vesicular sensor models indicate that a high concentration of EGTA decreases Ca2+ and vesicular release in the nanodomain of single channels. We found that a key determinant of the effect of EGTA on neurotransmitter release is the saturation of the vesicular sensor. When the sensor is saturated, the reduction in the Ca2+ concentration by EGTA is masked. By contrast, when the sensor is in a linear range, even a small reduction in Ca2+ by EGTA can decrease vesicular release. In proximity to a channel, the vesicular sensor is often saturated for a long voltage step, but not for a brief Ca2+ influx typically evoked by an action potential. Therefore, when EGTA is used as a diagnostic tool to probe the coupling distance, care must be taken regarding the presynaptic Ca2+ entry duration as well as the property of the vesicular Ca2+ sensor.

Chromogenic vesicles for aqueous detection and quantification of Hg2+/Cu2+ in real water samples

Mercury and copper are toxic environmental pollutants, which pollutes air, water and land posing a sever threat to the human health. For instant valuation, a qualitative method (colorimetric) for recognition of these analytes can be a better choice. However, for precise measurement, below the threshold value, a quantitative method is needed. Herein, we present the aqueous and visual detection of these analytes through the polymer vesicles functionalized with rhodamine based chemical sensor 2-(6-bromobenzo[d]thiazol-2-yl)-3′,6′-bis(diethylamino)spiro[isoindoline-1,9′-xanthen]-3-one (BTDX). The synthesized vesicular sensor exploits the self-assembling nature of the alternating copolymer followed by robust coordination of metallic ions with highly electronegative atoms i.e. oxygen nitrogen and Sulphur. During the sensing process, this interaction leads to the spirolactam ring opening of xanthene moiety attached to the surface of the polymeric vesicular sensor. This ring opening owes to the substantial increase in the spectral pattern (fluorescence and UV–Visible) of the vesicular sensor. Consequently, this binding behavior leads to the competitive cation study which result into the transformation of P(DO-a-DTODT)-g-BTDX@ vesicles (colorless) to the P(DO-a-DTODT)-g-BTDX-Hg2+/Cu2+ complexed vesicle (pink colored) solutions. This colorimetric transition evidence the naked eye detection of these analytes. Additionally, the lower limit of detection was calculated as low as 20 nM for Hg2+ and 30 nM for Cu2+. Finally, seawater was employed to quantify these environmental pollutants. The findings reveal that the vesicular sensor has excellent ability to quantify these pollutants in terms of %age recovery. The calculated value was not less than 95%.

Self-assembly of alternating copolymer vesicles for the highly selective, sensitive and visual detection and quantification of aqueous Hg2+

In recent years, there has been an ever-increasing demand to develop highly sensitive and selective colorimetric detection systems to tackle the growing threat of potentially toxic mercuric ions (Hg2+) exposure at the global level. However, most of the reported chemosensors for Hg2+ detection worked only in organic or in mixed solutions (organic/aqueous). The properties of the reported aqueous chemosensors for Hg2+ are not satisfactory. Herein, we take the advantage and present the first vesicular chemical sensor for the aqueous detection of Hg2+ with a high efficiency and selectivity. The vesicles were obtained through the aqueous self-assembly of the newly synthesized amphiphilic alternating copolymer poly(2, 3-dihydroxybutylene-alt-2,3-dihydroxybutylenedithioether) [P(DHB-a-DHBDT)] grafted with 2-(5-bromopyridine-2-yl)-3′,6′-bis(diethylamino)spiro[isoindoline-1,9′-xanthene]-3-thione (PST) probes. After the addition of Hg2+, the colorless aqueous solution of the vesicles changed into pink color accompanied by the significant enhancement of photophysical (emission and absorption) intensities at 580 nm and 559 nm, respectively. This color transition from colorless to pink allows the “bare-eye” detection of Hg2+ ions in the aqueous medium. The vesicular sensor also shows high selectivity for Hg2+ detection among miscellaneous metal cations. The detection limit (LOD) is about 53.0 nM, which is approximately one or two order of magnitude higher than those of the reported aqueous Hg2+ chemosensors. The mechanism study indicates the significant enhancement of emission and absorption intensities in response to Hg2+ should be attributed to the spirolactam ring opening via photoinduced electron transfer (PET) of xanthene moiety in the PST probes. Most importantly, the newly developed polymeric vesicle sensors shows great potential for the detection and quantification of Hg2+ with excellent selectivity in real water samples with the percentage recovery of 102–98%.

EP 86. Interneuron synaptopathy induced by the pro-inflammatory cytokine LIF in developing neocortex

An inflammatory episode during brain development is discussed as first hit which could trigger a higher susceptibility for epilepsy or development of mental disorders. We addressed the early developmental actions of an IL-6 type pro-inflammatory cytokine, leukemia inhibitory factor (LIF) on cortical maturation both in vivo and in slice cultures. A rather modest enhancement of LIF signaling was used as a proxy for an early postnatal inflammation. It resulted in a dramatic interneuron synaptopathy. Our results indicate that LIF impairs development of cortical interneuron subsets and causes a lasting imbalance of excitation and inhibition. In particular, LIF not only downregulates the expression of the TrkB receptor ligand NT4, but concurrently prevents the neurotrophins from activating the MAP kinase pathway. As a consequence, strictly TrkB-dependent cortical inhibitory GABA-ergic interneurons, in particular fast-spiking basket (B) and chandelier (C) neurons are severely affected. They display an underdevelopment of the somatodendritic domain, less and smaller presynaptic boutons, a reduced expression of the calcium buffer parvalbumin, the voltage-gated potassium channel Kv3.2, the ultrafast vesicular calcium sensor synaptotagmin-2, and glutamate decarboxylase isoform GAD-65 which synthesized GABA for phasic inhibition. These presynaptic proteins are essential for the fast-spiking properties and a highly synchronous GABA release, both being critical determinants for neuronal oscillations in the cognitive gamma frequency band. Also pyramidal cells are altered: dendritic spines are lower in density and less mature, GABA A R α 1 at basket cell terminals and α 2 at chandelier cell terminals are reduced in expression, the axon initial segment is shorter and its core scaffolding protein sIV-spectrin is reduced. The presynaptic deficits (outlined in the graphical abstract with left: healthy; right: LIF / inflammation) suggest a serious impairment of inhibition, and calcium imaging indeed reveals a hyperexcitable network. A set of recovery experiments reveals a surprisingly slow recovery of the affected proteins, and intriguingly, synaptotagmin-2 entirely fails to recover. In summary, our study suggests LIF as a negative upstream modulator of TrkB signaling. The impaired trophic support results in a maldevelopment in particular of fast-spiking interneurons, a deficit of inhibition and cortical hyperexcitability.

Smart stimuli-responsive fluorescent vesicular sensor based on inclusion complexation of cyclodextrins with Tyloxapol

Novel fluorescent vesicles based on inclusion complexes of β-cyclodextrins (β-CD) with Tyloxapol were constructed.

A novel fluorescent vesicular sensor for saccharides based on boronic acid–diol interaction

A novel amphiphile containing two functional groups of both naphthalene and boronic acid, 2-(hexadecyloxy)-naphthalene-6-boronic acid (HNBA), has been synthesized. Scanning electron microscopy (SEM) indicated the formation of bilayer vesicles in the ethanol/water solution (Phi=0.6). Differential scanning calorimetry (DSC) established the presence of crystal-to-liquid crystal transition at 63.36 degrees C. The vesicular fluorescence properties upon binding with carbohydrates have been studied in ethanol/water buffer at pH 7.4. Addition of saccharides to the vesicular solution, the fluorescent intensities of naphthalene in HNBA vesicles centered at 348 nm decreased dramatically with increasing concentration of saccharides. The change tendency of fluorescent intensities of the HNAB vesicles with concentration of saccharides followed in the order of fructose>galactose>maltose>glucose. The pH profiles of the fluorescence intensity were studied in the absence and in the presence of sugars. Also, the urine sample induced spectral changes of the HNBA vesicles were studied. These results suggest that the HNBA vesicles may be developed as a continuous monitoring and implantable fluorescence vesicular sensor, which might be applied in the practical field.

Glucose-responsive vesicular sensor based on boronic acid–glucose recognition in the ARS/PBA/DBBTAB covesicles

The amphiphile, 4-(4-dodecyloxybiphenyl-4-yloxy) butyl trimethylammonium bromide (DBBTAB), has a cationic group with quaternary ammonium salt, which can self-organize into vesicles in dilute aqueous solutions. The alizarin red S (ARS) with a negatively charged group is attracted electrostatically to the positively charged surface on the DBBTAB vesicles to form covesicles. By taking advantages of the features, a vesicular fluorescent sensor was prepared based on phenylboronic acid (PBA)–glucose recognition in the aqueous ARS/PBA/DBBTAB covesicles. The sensor was constructed with three constituents: PBA, DBBTAB amphiphile and ARS which served as the detector. The vesicular sensor enhanced the sensitivity to glucose by about seven- to eight-fold, compared with the same aqueous PBA/ARS solution, which was ascribed to the increased local concentrations of glucose on the surface of vesicles. The vesicular sensor may be available for detection of saccharides in biological systems.

A Highly Sensitive Trigger

Neurotransmitter release from vesicles in the presynaptic terminal is triggered by a brief increase in calcium that is triggered by an action potential. There has been a long debate concerning the sensitivity of the vesicular calcium sensor for mammalian central synapses and the minimal calcium concentration that is necessary to start the subsequent molecular events that lead to vesicle fusion with the plasma membrane. Bollmann et al . measured laser-induced release of caged calcium in a rat auditory brainstem synapse and found that increases in calcium concentrations of 1 µM evoked release. The authors' analysis indicates that a brief spike of 10 µM calcium would be sufficient to match the rate of synaptically evoked neurotransmitter release. This result implies that the calcium sensor in the presynaptic terminal has a high calcium affinity. Bollman, J.H., Sakmann, B., and Borst, J.G.G. (2000) Calcium sensitivity of glutamate release in a calyx-type terminal. Science 289 : 953-957. [Abstract] [Full Text]