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  • Open access
  • 87 Reads
Label-Free Anti-human IgG Biosensor based on Chemical Modification of a Long Period Fiber Grating Surface

Biosensors are powerful allies for food safety, drug discovery, environmental monitoring, and clinical diagnosis. Optical biosensors are an active field of research worldwide, presenting rapid progress in recent years. In this perspective, optical biosensors based on refractometric sensing schemes have been developed with great successes in the last decades. Moreover, optical fibers (OF) based on evanescent wave sensing are an excellent platform to develop high-stability and high-sensitive optical biosensors. The quantitative and/or qualitative measurements result from the interaction of the analyte with the evanescent field of light at the fiber surface. It’s good biochemistry makes them appropriate for biochemical functionalization, creating very sensitive structures targeting viruses, drugs, and proteins. This work presents a method specially developed for the production of MIP, based on Stöber silica nanoparticles, immobilized in the surface of commercial SMF28 OF, serving has recognition elements for specific target molecules. The nanoparticles surface was functionalized by the introduction of an aminosilane (APTMS) followed by the covalent immobilization of the immunoglobulin G (IgG) from human serum. The antibody was activated by the EDC/NHS protocol to allow the interaction of the amine exposed groups, located on the surface of the silica nanoparticles, with the activated carboxyl acid groups of the IgG molecules. The resulting template was immobilized onto the surface of an OF. The sensing structure is based on long period fiber gratings (LPFGs), specially developed to allow the interaction of the electromagnetic wave with the target analytes through its evanescent field. The refractometric system comprises a Braggmetter unit (HBM, FiberSensing) working in a wavelength range from 1500 to 1600 nm, and a reference LPFG to correct possible false interactions. The resulting configuration was tested in the presence of anti-human IgG, recording the refractometric response of the modified LPFG in contact with different amounts of analyte.

  • Open access
  • 120 Reads
Group 14 Metallafluorenes for Lipid Structure Detection and Cellular Imaging

Lipid droplets (LD) are lipid-rich cellular organelles that play a critical role in energy metabolism and some disease pathology. Due to the highly diverse nature of lipid composition, it is difficult to address fundamental questions regarding their mechanism of action. Environmentally sensitive dyes have been shown to be useful in probing lipid dynamics, and there is ongoing interest in developing dyes that are nontoxic, photostable, and sensitive. Recently we evaluated a small library (4) of 2,7-disubstituted-alkynyl(aryl)-3,6-dimethoxy-9,9-diphenylsilafluorenes/germafluorenes with different -alkynyl(aryl) substituents for their potential as cellular fluorescent probes. These compounds are soluble in water and luminesce in aqueous solution. In this library, emission maxima differ by as much as 67 nm, providing wavelength tunability. Moreoever, these compounds exhibit remarkable quantum yields in hydrophobic environments (approaching 1.00) and dramatic increases in emission intensity in the presence of surfactants (up to 25x). Here we show that they are nontoxic to E. coli, S. aureus, and S. cerevisiae. Further, they exhibit significant emission enhancements in the presence of small unilamellar vesicles (SUVs) (2-6x). We also note that they luminesce in S. cerevisiae cells with strong photostability in vivo. These sila- and germafluorenes colocalize with the LD stain Nile Red in S.

  • Open access
  • 133 Reads
Improved sensors based on composite materials for cadmium, lead and copper determination

Water is fundamental for all the Earth’s living forms, and a key issue for social and economic development. Some of the metals that can be found in water are: Cu, Cd and Pb and a high concentration of these metals can have consequences on human health.

Many carbon materials are well-known conductive material, widely used in the fabrication of composite electrodes. In this work, diverse allotropic forms of carbon as graphite, multiwalled carbon nanotubes (MWCNTs) and reduced graphene oxide (rGO) were tested. Furthermore, these materials allow the construction of cheaper, smaller, portable, reliable, and easy to use devices, which can be easily modified by two routes, on surface or matrix. To use said composites electrodes for metal detection, Square Wave Anodic Stripping Voltammetry (SWASV) is the select technique, which consists in two steps. Fist, applying a potential to preconcentrate the analyte on the surface of the electrode and second the measurement is performed applying staircase potential and the current generated is recorded.

To increase the sensitivity of the composite sensor, it would be ideal to exploit the potential properties of mercury for metal detection by tuning electrode’s surface. Due to mercury’s hazardous properties and to reduce the amount used in polarography, the use of nanoparticles is a good option due to their properties. Mercury nanoparticles were used to modify the surface of the composite electrodes to improve electroanalytical sensor response.

  • Open access
  • 62 Reads
SERS-based sensor for diagnosis of sexually transmitted diseases: a study of clinical samples

Sexually transmitted diseases (STDs) refer to infections and syndromes caused by bacteria, viruses, protozoa. It is estimated that each year around 214 million people struggle with STDs caused only by bacteria: Chlamydia trachomatis (127 million) and Neisseria gonorrhoeae (87 million). That makes STDs an epidemic and can lead to numerous economic and health consequences. There are several methods that enable the diagnosis of STDs, but each of them has some limitations e.g.: Gram staining is characterized by its low detection rate while microbial culture requires time-consuming incubation and specific conditions for bacterial growth. Even the most recommended tests - nucleic acid amplification tests (NAATs) are very expensive and not every laboratory can afford them. For the above-described reasons, there is still a need to establish a rapid, reliable, and sensitive method for STDs diagnosis.

More recently, a lot of studies have been done presenting the great potential of the application of SERS (Surface-enhanced Raman Spectroscopy) in diverse fields including medicine and biology. SERS is a kind of fingerprint technique based on the inelastic scattering of incident light by molecules adsorbed on the roughened metal surface (SERS-active substrate). The phenomenon of the SERS technique originates mainly from two main mechanisms: electromagnetic (EM) and chemical.

In this study, we present that SERS-based sensor and chemometric analysis can be performed successfully in a direct and indirect manner for STD diagnosis. The indirect (confirmatory) approach is based on the identification of unknown pathogenic strain in the clinical samples, by comparison, its spectral image to other spectral images of different bacteria. While the direct one guarantees ultrafast diagnosis (up to 15 min) by classifying SERS spectra of clinical sample to the correct group by means of supervised technique (SIMCA, PLS1-DA). The undoubted advantage of this approach is simplified procedure while maintaining ultra-high sensitivity. Hence, both of these methods can compete with many currently used techniques.

This research may have a great impact on the biomedical applications since, the integration of SERS-based sensors with a small, portable Raman spectrometer could lead to the development of a handheld point-of-care device, which would enable the diagnosis of STD in an extremely short time [1].

[1] S. Berus et al. Patent Application P.436251, 2021

  • Open access
  • 126 Reads
Voltammetric nanodiamond-coated screen-printed immunosensor for the determination of a peanut allergen in commercial food products

Groundnuts, like peanuts, are commonly integrated into the Mediterranean dietary pattern, and their consumption has been recommended worldwide. However, reported cases of peanut allergy have increased and, therefore, commercial food tracking is essential, since in extreme cases peanut intake causes anaphylaxis. Efficient detection of peanut traces in food samples can be achieved using electrochemical immunosensors that benefit from their advantageous features such as high selectivity and sensitivity, low cost, and rapid detection. Because disposable screen-printed electrodes can be connected to portable devices, they can be used for in situ allergen analysis.

In the present work, a voltammetric immunosensor was developed to quantify a major peanut allergen, Ara h 1, using screen-printed carbon electrodes (SPCE) as transducers. Distinct carbon-based nanomaterials were tested, and nanodiamonds were selected for the nanostructuration of the transducer’s surface. A sandwich-type immunoassay was performed on the nanodiamond-coated SPCEs using an alkaline phosphatase-labelled detection antibody and a mixture containing an enzymatic substrate (3-indoxyl phosphate) and silver nitrate. The immunological interaction was detected through the (linear sweep) voltammetric stripping of the enzymatically deposited silver. A linear concentration range was established between 25 and 500 ng·mL−1 (ip = (0.027 ± 0.001) [Ara h 1] + (1.41 ± 0.31), r = 0.994, n = 5), with a sensitivity of 0.342 µA·mL·ng-1·cm-2. The limits of detection (LOD) and quantification (LOQ) were 0.78 and 2.6 ng·mL−1, respectively. Other allergens, non-target proteins and food product ingredients were tested to assess the selectivity of the immunosensor. Its applicability was evaluated by analysing a set of breakfast cereals, cookies, and energetic and cereal bars.

  • Open access
  • 235 Reads
A Case Study of Nitrate Reduction in Paper-Based Devices

Paper-based microfluidic technology is a relatively new field of research that provides low-cost platforms and sensors for point-of-care diagnostics. While the majority of research in this field has been for biomedical applications, more and more paper-based devices and platforms are being designed and developed for environmental applications such as water quality monitoring and assessment. One such application is the detection of nitrate in water samples. Colorimetric detection of nitrate by paper-based devices using the Griess assay requires the reduction of nitrate to nitrite before undergoing the reaction. In this paper, we measured the performance of a paper-based dip strip for detecting nitrate and nitrite by calculating its limit of detection and limit quantification. We also calculated the reduction efficiency of vanadium (III) chloride in the dip strip for detecting nitrate. Our results show that the reduction time of nitrate via vanadium (III) chloride is much longer than that when using zinc microparticles. Our results also show that the performance of the dip strip using vanadium (III) chloride for nitrate detection is not as good as more intricate paper-based devices that have a separate reaction zone with zinc microparticles. The limits of detection and quantification calculated were 3.352 ppm and 7.437 ppm and the nitrate reduction efficiency varied over the range of nitrate concentrations tested.

  • Open access
  • 64 Reads
Applied voltage variation’s effect in LbL sensors while detecting 17α-ethinylestradiol in water samples

In this work, the effects of differing voltage levels applied to interdigitated gold electrodes (IDE) sensor devices with thin-film polyelectrolyte layers for the detection of 17α-ethinylestradiol (EE2) were studied. EE2 is a synthetic hormone present in the composition of oral birth control pills, which are a frequently used contraceptive. EE2 through natural bodily excretions finds its way into wastewater, which in turn are led to wastewater treatment plants where the treatments conducted are not able to completely remove EE2 from the water. This treated water with trace amounts of the hormone is then released into natural bodies of water where it has a pernicious impact on the life cycles of both flora and fauna, disrupting various ecosystems. Through the pairing of IDE containing layer-by-layer (LbL) thin-films with impedance spectroscopy, electrical measurements of solutions of mineral water (MW) (pH = 5.7 ± 0.3) and tap water (TW) (pH = 6.8 ± 0.1) spiked with a concentration of 10-12 M of EE2 were conducted while applying varying AC voltages to the IDE sensors from 25 to 1000 mV. To better understand the data obtained during this work, several spectra were plotted among which is the loss tangent spectra. From these plots, one can surmise (for both waters) that by increasing the voltage there is a decrease in the polarization of the thin-film sensors, which results in less responsive sensor devices. It was also possible to observe that the higher the voltage, the less reproducible the sensors tend to be.

  • Open access
  • 65 Reads
Characterization and comparison of the relative humidity response of hydromorphic polymers in Long-Period Fiber Grating structures

Relative humidity monitorization is a process of extreme importance on both scientific and industrial applications, and while many types of sensors have been developed, the typical low-cost capacitive or resistive structures may display some flaws, such has not being immune to electromagnetic radiation, and not fit to extreme and harsh environments (such as underwater applications). In order to solve some of these limitations, optical fiber sensors have been developed, consisting of optical structures associated with a humidity responding polymer, resulting in a measurable change in the optical spectrum.

In this work, a preliminary study of three different humidity responding polymers in association with Long period Fiber Gratings (LPFG) is reported, along with a complete description of the fabrication methods, relative humidity performance testing and result interpretation. The polymers used are Poly(vinyl alcohol), Poly(ethylene glycol) and Hydromed™ D4, resulting in sensors with different properties and working ranges. The interpretation of the results presented is aided by the usage of numerical simulations of the LPFG structures, enabling a better understanding of the acquired data and defining future work to be carried out.

  • Open access
  • 71 Reads
An Inkjet-printed amperometric H2S sensor for environmental applications

Hydrogen sulfide (H2S) is a highly toxic and dangerous compound, capable of causing severe health problems after prolonged exposure even at low concentrations. It is a gas, slightly solvable in water at acid pH. Nonetheless, as pH increases its labile protons are lost and it becomes the more soluble HS- ion. It appears in wastewater treatment plants and gas treatment bio-scrubbers and is still highly pollutant and hazardous. Thus, it is of critical importance to develop effective methods to monitoring H2S in biological treatment process and water systems.

Inkjet printing technology has been proven in the recent years as an economic, fast, reproducible and highly versatile method of mass-producing micro-electrodes. Those can themselves be made of a large variety of materials, from metals to polymers. Tuned with the appropriate transductors, many electrodes can become sensors for analytes of interest. Considering the hazards produced by chemicals like H2S, miniaturized systems like this are becoming the new sensing platforms for tracking pollutants.

Herein, an easy to produce, low-cost, miniaturized and inkjet-printed amperometric H2S sensor is presented. A gold electrode, coupled to a conductive track of silver, is modified with a mixture of Single-Walled Carbon Nanotubes (SWCNTs), Poly(VinylAlcohol) (PVA) and Poly(DiallylDimethylAmmonium Chloride) (PDDA). It detects HS- by oxidizing it into elemental sulfur (S0), recording the produced current from this reaction. It has an effective working pH range of 6.5-13 and a wide linear range response from 6 µM to 592 µM of HS-. Tests show that the sensor is also capable of working on complex samples, such as reactor media.

  • Open access
  • 60 Reads
Quasireversible maximum under conditions of novel electrochemical techniques

Information on the kinetics and mechanisms of electrode processes is most often obtained using conventional electrochemical techniques. The high quality of the obtained data and good sensitivity are guaranteed by techniques that minimize the impact of capacitive current. Among pulse techniques, we can distinguish square wave voltammetry, which, unfortunately, due to the complexity of the results, causes difficulties in data interpretation.

In order to simplify electrokinetic and mechanistic studies, the potential modulation applied to the working electrode under SWV conditions was modified. The underlying staircase potential, which is typical for SWV, is replaced with constant mid-potential. Any subsequent changes involve the modification of the basic parameters i.e. amplitude and frequency. The resulting emergence of three novel electrochemical techniques enable receive of information on the rate of reaction in an alternative, simple and fast procedures. These techniques are based on the measurement of the characteristic dependence of the current as a function of the applied frequency or amplitude in a form of so-called quasireversible maximum based either on amplitude or frequency. The position of the quasireversible maximum provides important data on electrode reaction kinetics because it enables estimation of the standard rate constant.

The proposed novel electrochemical techniques were applied in real electrochemical systems to assess the possible recording of a quasireversible maximum in the case of simple electrode mechanisms.