Synthetic Physiological Fluid Research Articles

Static quenching and inner-filter effect assisted turn-off fluorescence sensor for the determination of hepatobiliary biomarker bilirubin based on luminescent copper nanoparticles

The determination of bilirubin level is a crucial aspect of medical diagnosis and plays a significant role in assessing the health of an individual, particularly in relation to the liver and blood. This paper discusses the development of a facile, cost-effective and sensitive turn-off fluorescence sensing platform for the determination of bilirubin based on highly stable and luminescent copper nanoparticles protected by ascorbic acid (AACuNPs). The fluorophore was characterised by UV–Visible spectrophotometry, FT-IR, XPS and EDX spectroscopic techniques as well as by TEM and zeta potential analysis. Bilirubin could selectively quench the fluorescence intensity of AACuNPs linearly in the concentration range from 1.00 × 10-5 M to 5.00 × 10-7 M and the limit of detection was obtained to be 2.48 × 10-7 M. The mechanism underlying the sensing of bilirubin has been explored with the help of various experimental techniques and is found to be a static quenching mechanism assisted by the inner filter effect. Moreover, the synthesized fluorophore has proved to be successful in the determination of bilirubin in synthetic physiological fluids. High selectivity and very low interference from probably coexisting species in the physiological fluids also verify the reliability of the sensor for the determination of bilirubin.

Fabrication and Comprehensive Comparison of the Performance of Chemically Modified GCE and SPCE for the Simultaneous Determination of Uric Acid and Vanillylmandelic Acid

Uric acid (UA) and Vanillylmandelic acid (VMA) are two important biomarkers that can significantly account for certain pathological conditions in our body. A novel and efficient electrochemical sensor has been fabricated for the simultaneous determination of UA and VMA based on screen printed carbon electrodes chemically modified with a nanocomposite of reduced graphene oxide and poly(L-threonine) conducting polymer (rGO- p(Thr)/SPCE). The fabricated sensor has been well characterized and various experimental conditions were optimized to avail maximum performance of the sensor towards the determination of UA and VMA. In addition, the sensor's performance was rationally analysed and compared with the same sensor fabricated on a conventional glassy carbon electrode (rGO- p(Thr)/GCE) to understand how the change in electrode substrate affects the sensor's performance. Studies revealed that although both of the sensors can be successfully applied for the simultaneous determination of UA and VMA over wide linear ranges with lower detection limits, better sensitivity was acquired when rGO- p(Thr)/GCE was used. On the other hand, modification of SPCE provided greater reduction in electrooxidation potential of UA and VMA than GCE. Electroactive surface area changes in GCE and SPCE upon modification showed different trends, whereas study on mechanistic aspects of electrooxidation exhibited similar results. Since SPCE is more of practical relevance considering the ease of miniaturization and applicability in on-site analysis, studies on interference by probable coexisting species and applicability of the sensor in synthetic physiological fluids were also successfully carried out on rGO-p(Thr)/SPCE.

Folic acid capped bimetallic nanoparticle based fluorescence sensor for the nanomolar determination of bilirubin

Folic acid capped Silver-Copper bimetallic nanoparticle (FA-AgCu BNP) based turn-off fluorescence sensor has been developed for the rapid and facile determination of a prominent disease biomarker, Bilirubin. FA-AgCu BNP has been characterised via Fluorescence spectroscopy, EDX, TEM, DLS, Zeta potential, UV–visible spectroscopy, FTIR spectroscopy and XPS techniques. Fluorescence quenching of FA-AgCu BNP has been observed in the presence of bilirubin which is due to the combined effect of static quenching and Inner filter effect. Different analytical parameters were optimised and under these conditions, the sensor showed good selectivity towards bilirubin and attained a wide linear range from 2.00 × 10-5M to 1.00 × 10-7M with a limit of detection of 5.53 × 10-9 M. Practical utility of the proposed sensor has been illustrated in synthetic physiological fluids by spike recovery analysis and the obtained results were validated using classical spectrophotometric method.

Tryptophan capped gold–silver bimetallic nanoclusters-based turn-off fluorescence sensor for the determination of histamine

Tryptophan capped gold-silver bimetallic nanoclusters (Trp-Au/Ag BNCs) based turn-off fluorescence sensor has been developed for the simple and rapid determination of histamine. Sensor parameters such as the effect of solvent, irradiation time etc. were optimized and further studies were done using these results. Fluorescence quenching of BNCs happens with the incremental addition of histamine. This might be due to the aggregation of BNCs induced by the electrostatic force of attraction between the negatively charged BNCs and amino functional groups of histamine. The sensor showed good sensitivity for the determination of histamine with a linear range of 8.5 × 10−5 M to 4.0 × 10−6 M and a limit of detection (LOD) of 9.0 × 10−7 M. Practical utility of the proposed sensor has been proved through spike recovery analysis in synthetic physiological fluids.

Development of Molecularly Imprinted poly(Phenol) Membrane Based Electrochemical Sensor for The Selective Determination of Guanine

This article describes the development of a simple, selective and sensitive molecularly imprinted polymer (MIP) based voltammetric sensor for guanine (Gua). The recognition element, MIP was fabricated by electropolymerization of the functional monomer phenol in presence of Gua onto the surface of a poly(L- Glutamic acid) (pGlu) modified glassy carbon electrode (GCE). Extraction of the template molecules, Gua from the poly(phenol) layer was carried out using a solvent mixture of ethanol and 10% acetic acid at 1:1 (v/v) ratio. Various experimental parameters determining the performance of the sensor were optimized and under these conditions the proposed sensor responds linearly to the concentration of Gua in the range from 8.00 × 10−5 M to 2.00 × 10−5 M and 1.00 × 10−5 M to 5.00 × 10−7 M with the limit of detection as low as 8.00 × 10−8 M. The sensor exhibits excellent selectivity, reproducibility and stability. It was successfully applied in synthetic physiological fluids in order to verify its practical utility.

A dual channel optical sensor for biliverdin and bilirubin using glutathione capped copper nanoclusters

A simple, highly selective and cost-effective colorimetric as well as fluorimetric sensor for the bile pigments, biliverdin (BVD) and bilirubin (BLR) has been developed using glutathione stabilized copper nanoclusters (GSH-CuNCs). Sensing has been achieved via the formation of a non-fluorescent ground state complex between the nanoprobe and analytes. Different sensor parameters were optimized and under these conditions, highly sensitive determination of BVD/BLR in wide linear ranges has been obtained in a dual responsive manner. Practical utility of the developed sensor has also been demonstrated in synthetic physiological fluids.

A passive direct methanol fuel cell as transducer of an electrochemical sensor, applied to the detection of carcinoembryonic antigen

This work describes an electrochemical sensor with a biomimetic plastic antibody film for carcinoembryonic antigen (CEA, an important biomarker in colorectal cancer), integrated in the electrical circuit of a direct methanol fuel cell (DMFC), working in passive mode and used herein as power supply and signal transducer. In detail, the sensing layer for CEA consisted of a Fluorine-doped Tin Oxide (FTO) conductive glass substrate – connected to the negative pole side of the DMFC – with a conductive poly (3,4-ethylenedioxythiophene) (PEDOT) layer and a polypyrrol (PPy) molecularly-imprinted polymer (MIP), assembled in-situ. This sensing element is then closed using a cover FTO-glass, hold in place with a clip, connected to the positive side of the DMFC. When compared with control DMFCs, the power curves of DMFC/Sensor integrated system showed decreased power values due to the MIP layer interfaced in the electrical circuit, also displaying high stability signals. The DMFC/Sensor was further calibrated at room temperature, in different medium (buffer, a synthetic physiological fluid model and Cormay® serum), showing linear responses over a wide concentration range, with a limit of detection of 0.08 ng/mL. The DMFC/Sensor presented sensitive data, with linear responses from 0.1 ng/mL to 100 μg/mL and operating well in the presence of human serum.Overall, the results obtained evidenced the possibility of using a DMFC as a transducing element in an electrochemical sensor, confirming the sensitive and selective readings of the bio (sensing) imprinted film. This integration paves the way towards fully autonomous electrochemical devices, in which the integration of the sensor inside the fuel cell may be a subsequent direction.

Corrosion and metal release investigations of selective laser melted 316L stainless steel in a synthetic physiological fluid containing proteins and in diluted hydrochloric acid

The corrosion and metal release characteristics of additively manufactured stainless steels are key factors for their applicability in biomedical applications. The effect of building direction on the microstructure, corrosion behavior and metal release of selective laser melted (SLM) AISI 316L stainless steel were therefore investigated in a protein-rich synthetic body fluid (PBS+BSA, pH 7.3) and in diluted hydrochloric acid (HCl, pH 1.5). A multi-analytical approach was applied to characterize SLM 316L surfaces printed in different building directions (denoted XY and XZ) and a post heat treated SLM surface (XZ-HT) compared with wrought surfaces. All SLM specimens revealed an austenitic microstructure without any amounts of δ-ferrite and without large-angled grain boundaries in contrast to the wrought 316L surface. The building direction strongly affected the grain size distribution due to the temperature gradients in the melt pools. The SLM 316L specimens released initially slightly less Fe, Cr and Ni compared with the wrought 316L specimen. Slightly less metal was released from the heat treated SLM specimen (XZ-HT) specimen compared to the other SLM specimens. Relatively high amounts of released Cr were observed in PBS+BSA, most probably attributed to protein-bound Cr, whereas substantially more Ni was released in HCl compared to PBS+BSA due to pitting corrosion and a reduced surface oxide thickness. The surface oxide composition of as-printed SLM specimens was strongly dependent on the building direction and the post heat treatment, whereas no differences were observed after abrasion either among the SLM specimens or compared with the wrought 316L specimen. Cr became in all cases enriched within the outermost surface oxide in PBS+BSA and strongly enriched in the HCl solution, coupled to a strongly reduced amount of released metals with time. The heat treated SLM specimen (XZ-HT) gained a superior charge transfer resistance, the lowest passive current density, and the highest OCP value among all specimens. In HCl, the SLM specimens showed a lower pitting susceptibility compared to the wrought specimens. No pitting was observed in PBS+BSA. No differences in corrosion or metal release characteristics were observed related to the building direction of abraded SLM specimens.

A study of zinc ions immobilization by β-lactoglobulin

The aim of the study was to immobilize zinc ions by β-lactoglobulin (βLG) micelles. The investigation focused on physicochemical properties of β-lactoglobulin and zinc-β-lactoglobulin complexes as well as the stability of the obtained complex in synthetic physiological fluids. Kinetic and isothermal studies of zinc ion immobilization by βLG were conducted based on batch sorption approach, while the mechanism of binding zinc ions to βLG was determined and described by application of several kinetic and isotherm models, such as zero order, first and pseudo-first order, intraparticle Weber-Morris diffusion, Langmuir and Freundlich models. The nature of binding/immobilization of zinc ions to βLG was determined with instrumental complementary analysis by using the spectrometric, spectroscopic, microscopic, thermal and X-ray diffraction methods. The results revealed that zinc ion binding to βLG is a heterogeneous process which consists of three main stages: the stage one was associated with rapid sorption of zinc ions on the surface of βLG micelles, while stages two and three resulted from intramolecular diffusion of zinc ions. Moreover, based on instrumental and stability study it was proven that acidic (Glu, Asp) and aromatic (Tyr, Trp, Phe) amino acid groups participate in formation of Zn-βLG complex as a metallocomplex with nutraceutical potential.

Separation of aflatoxin B1 from synthetic physiological fluids using talc and diatomite: Kinetic and isotherm aspects.

The objective of the study was to examine adsorption of the aflatoxin B1 from synthetic gastric fluid and synthetic intestinal fluid by talc, raw and calcined diatomite. The kinetic and equilibrium adsorption processes were studied in the batch adsorption experiments applying high performance liquid chromatography for the aflatoxin B1 determination. The kinetic study showed a very fast adsorption of the aflatoxin B1 onto the selected adsorbents from the both physiological fluids with reaching equilibrium within 1-15min. The aflatoxin B1 was almost completely adsorbed in initial linear step of the kinetic process that can be described well by the zero-order kinetics model. The experimental data of the equilibrium adsorption were characterized using the Langmuir and Freundlich isotherm models. The high adsorption effectiveness was found in a range of 90%-100% and 60%-100% for the diatomite samples and the talc respectively at the initial concentrations of the aflatoxin B1 as 31-300ng/mL. The possible mechanisms of the aflatoxin adsorption onto the used mineral adsorbents are also discussed in the work.

Bioglass implant-coating interactions in synthetic physiological fluids with varying degrees of biomimicry.

Synthetic physiological fluids are currently used as a first in vitro bioactivity assessment for bone grafts. Our understanding about the interactions taking place at the fluid–implant interface has evolved remarkably during the last decade, and does not comply with the traditional International Organization for Standardization/final draft International Standard 23317 protocol in purely inorganic simulated body fluid. The advances in our knowledge point to the need of a true paradigm shift toward testing physiological fluids with enhanced biomimicry and a better understanding of the materials’ structure-dissolution behavior. This will contribute to “upgrade” our vision of entire cascades of events taking place at the implant surfaces upon immersion in the testing media or after implantation. Starting from an osteoinductive bioglass composition with the ability to alleviate the oxidative stress, thin bioglass films with different degrees of polymerization were deposited onto titanium substrates. Their biomineralization activity in simulated body fluid and in a series of new inorganic–organic media with increasing biomimicry that more closely simulated the human intercellular environment was compared. A comprehensive range of advanced characterization tools (scanning electron microscopy; grazing-incidence X-ray diffraction; Fourier-transform infrared, micro-Raman, energy-dispersive, X-ray photoelectron, and surface-enhanced laser desorption/ionization time-of-flight mass spectroscopies; and cytocompatibility assays using mesenchymal stem cells) were used. The information gathered is very useful to biologists, biophysicists, clinicians, and material scientists with special interest in teaching and research. By combining all the analyses, we propose herein a step forward toward establishing an improved unified protocol for testing the bioactivity of implant materials.

Structure and Degradation Behaviour of Calcium Phosphate Glasses

Some studies have shown a relationship between glass structure and in vitro mineralization, generally associated with the rate of glass degradation, nature of released ions and subsequent Ca-P precipitation on glass surfaces when immersed in a Simulated Body Fluid (SBF). The knowledge of the ionic species distribution in glasses and of the involved bond strengths can be used to assess the in vitro behaviour of a glass. The role of ions such as silicon or titanium is of major importance for the development of new compositions and also for the control of glass degradation behaviour. A comparative study with two calcium phosphate glasses series was performed: Both glasses series – one with Si and another with Ti – include P2O5 and alkaline earth ions in their compositions. Surface reactivity of glasses from the SiO2-containing system have been studied in SBF showing the precipitation of a Ca-P surface layer that increases with increasing MgO/CaO ratio. In glasses from the TiO2-containing series it is shown that the increase of TiO2 contributes for the stabilization of the glass network thus allowing the control of their degradation rate when immersed in SBF. The relationship between structural features of these calcium-phosphate glasses and their degradation behaviour in SBF is discussed in terms of the structural role of Si and Ti ions. It is concluded that glasses with less interconnected species favour the Ca-P surface precipitation. The understanding of this relationship in synthetic physiological fluids is expected to allow the tailoring of glass degradation rates in complex biological systems.

Phytate inhibits bovine pericardium calcification in vitro

The present study examined the inhibitory effects of pyrophosphate, etidronate, and phytate on bovine pericardium calcification in vitro. Bovine pericardium was glutaraldehyde fixed and then placed in a flow chamber in the presence of a synthetic physiological fluid alone (control) or the fluid plus various concentrations of pyrophosphate, etidronate, or phytate. Following a 96-h incubation, fragments were removed and assayed for calcification by measuring calcium and phosphorus levels. The data indicated that both pyrophosphate and etidronate at 1 mg/l (5.75 and 4.95 microM, respectively) inhibited bovine pericardium calcification, whereas neither agent had an effect at 0.5 mg/l (2.87 and 2.47 microM, respectively). Phytate was the most potent inhibitor of calcification, and the effects of this agent were apparent at levels as low as 0.25 mg/l (0.39 microM). While pyrophosphate, etidronate, and phytate were all able to inhibit bovine pericardium calcification in vitro, phytate was found to be the most effective.

05/01773 Surface behaviour of high MgO-containingglasses of the Si&z.sbnd;Ca&z.sbnd;P&z.sbnd;Mg system in a synthetic physiological fluid

The combined effects of high helium transmutation rates with the displacement damage produced by high energy fusion neutrons remains the key issues in the evaluation of the performance and lifetime limits of candidate vanadium alloys for fusion first-wall structure applications. A dynamic helium charging experiment (DHCE) has been developed as a unique method for investigating the effects of fusion-relevant helium generation rates on the properties of vanadium alloys irradiated in a fission reactor neutron spectrum. In this simulation, decay of tritium in the vanadium alloy to helium during fission reactor irradiation is used to provide constant He/displacement damage ratios characteristic of a fusion neutron environment. A proof-of-principle experiment (DHCE-1) was conducted in the FFTF reactor. Detailed calculations of the predicted helium concentrations in unalloyed vanadium and the reference V–4Cr–4Ti alloy included in the DHCE-1 indicate quite good agreement with experimental results and demonstrate the validity of the DHCE technique.

Self-assembling peptide amphiphile nanofiber matrices for cell entrapment

We have developed a class of peptide amphiphile (PA) molecules that self-assemble into three-dimensional nanofiber networks under physiological conditions in the presence of polyvalent metal ions. The assembly can be triggered by adding PA solutions to cell culture media or other synthetic physiological fluids containing polyvalent metal ions. When the fluids contain suspended cells, PA self-assembly entraps cells in the nanofibrillar matrix, and the cells survive in culture for at least three weeks. We also show that entrapment does not arrest cell proliferation and motility. Biochemical and ultrastructural analysis by electron microscopy indicate that entrapped cells internalize the nanofibers and possibly utilize PA molecules in their metabolic pathways. These results demonstrate that PA nanofibrillar matrices have the potential to be used for cell transplantation or other tissue engineering applications.

Surface behaviour of high MgO-containing glasses of the Si–Ca–P–Mg system in a synthetic physiological fluid

Two glasses of the Si–Ca–P–Mg system with low SiO 2 content (25 and 29 mol%) and high MgO contents (31 and 36 mol%, respectively) have been immersed in a Kokubo’s synthetic physiological solution for different times up to 30 days. The surface modifications of the glasses were observed by SEM and the changes in the surface composition followed by EDS. ICP was used to assess the evolution of ionic concentrations in the solution, namely Ca and P. It was observed that both glasses induced the precipitation of Ca–P rich layers on their surfaces, although these were poorly attached to the glass substrate. Ca and P ions required for the apatite formation were mainly provided by the composition of the glass, which was severely dissolved in the solution. The observed apatite-forming ability of these glasses, notwithstanding their high MgO content, suggests that further improvements at the surface and in the glasses can lead to attractive potentially bioactive materials.

Dual pH durability studies of man-made vitreous fiber (MMVF).

Dissolution of fibers in the deep lung may involve both extracellular and intracellular mechanisms. This process was modeled in vitro for each environment using an experimental flow-through system to characterize both total dissolution and specific chemical changes for three representative MMVF's: a glasswool, a slagwool, and a refractory ceramic fiber (RCF). Synthetic physiological fluids at pH 4 and at pH 7.6 were used to simulate macrophage intraphagolysosomal, and extracellular environments, respectively. Actual commercial fiber, sized to rat-respirable dimension, having an average fiber diameter of 1 micron and an average length between 15 and 25 microns, was used in the experiments. Fiber dissolution was monitored through change in chemistry of the fluid collected after percolation at a constant rate through a thin bed of sample. There are great differences in total fiber dissolution rates for the different fibers. Slagwool and RCF dissolve more rapidly at pH 4 than at pH 7.6, while the reverse is true for glasswool. Dissolution is sometimes accompanied by a noticeable change in fiber morphology or dimension, and sometimes by no change. There is strong dependency on pH, which affects not only total fiber dissolution, but also the leaching of specific chemical components. This effect is different for each type of fiber, indicating that specific fiber chemistry largely controls whether a fiber dissolves or leaches more rapidly under acidic or neutral conditions. Both total dissolution rates and calculated fiber composition changes are valuable guides to interpreting in vivo behavior of man-made vitreous fibers, and demonstrate the usefulness of in vitro acellular experiments in understanding overall fiber persistence.