High NIR-purity index single-walled carbon nanotubes for electrochemical sensing in microfluidic chips

Raman spectroscopy-based microfluidic platforms: A promising tool for detection of foodborne pathogens in food products

Rapid and sensitive detection of foodborne pathogens in food products is paramount for ensuring food safety and public health. In the ongoing effort to tackle this issue, detection methods are continually researched and upgraded to achieve rapidity, sensitivity, portability, and cost-effectiveness. This review addresses the critical need for improved technique by focusing on Raman spectroscopy-based microfluidic platforms, which have shown potential in revolutionizing the field of foodborne pathogen analysis offering point-of-care diagnosis and multiplex detection. The key problem lies in the persistent threat of compromised food quality and public health due to inadequate pathogen detection. The review elucidates the various trapping strategies employed in a microfluidic platform, including optical trapping, electrical trapping, mechanical trapping, and acoustic trapping for the capture of microbial cells. Subsequently, the review delves into the key aspects of the application of microbial detection in food products, highlighting recent advances and challenges in the field. The integrated technique allows point-of-care application assessment, which is an attractive quality for in-line and real-time detection of foodborne pathogens. However, the application of the technique in food products is limited and requires further research to combat the complexity of the food matrix, reduced costs of production, and ensure real-time use for diverse pathogens. Ultimately, this review aims to propel advancements in microbial detection, thus promoting enhanced food safety through state-of-the-art technologies.

Quantification and removal of carbonaceous impurities in a surfactant-assisted carbon nanotube dispersion and its implication on electronic properties

Carbonaceous impurities (CIs) affect the optoelectronic properties as well as the ability to use absorption spectroscopy to estimate the metallic content of a single-walled carbon nanotube (SWNT) dispersion. Therefore, a method for the accurate quantification and removal of CIs is required. We have devised methods to characterize and quantify CIs present in SWNT batches and to determine the effects of CIs on the optical and electrical properties of SWNT. Quantitative determination of CIs stems from the finding that chloroform selectively disperses CIs present in SWNT batches. CIs separated by dispersing the as-purchased SWNT batch in chloroform have the morphology of defective and agglomerated few-layered graphenes, whose sizes and locations depend on SWNT batches. Moreover, CIs exhibit a featureless UV-vis-mid-wavelength IR (MWIR) absorption curve and an extinction coefficient comparable to graphenes and show difference with carbon black, which is frequently used as the CI reference. The MWIR region that shows least absorptions caused by the transition of various SWNT types was utilized to assess the significant contribution made by CIs present in a surfactant-assisted SWNT dispersion, showing about 12-19 wt% of CIs in various SWNT dispersions. In addition, the extraction of CIs with chloroform results in a highly purified SWNT batch without any diameter distribution change originating from oxidative damage as compared to the commercially available purified SWNT batch. Finally, we found that increasing the weight of CIs present in a SWNT dispersion strongly lowers the thermal conductivity of a SWNT film when compared with the electrical conductivity. This study provides a way to understand the negative effects that CI has on the optoelectronic properties of SWNTs as well as the beneficial effects of excluding ubiquitous CIs in SWNTs batches.

Effect of nanocellulose polymorphism on electrochemical analytical performance in hybrid nanocomposites with non-oxidized single-walled carbon nanotubes

Two cellulose nanocrystals/single-walled carbon nanotube (CNC/SW) hybrids, using two cellulose polymorphs, were evaluated as electrochemical transducers: CNC type I (CNC-I/SW) and CNC type II (CNC-II/SW). They were synthesized and fully characterized, and their analytical performance as electrochemical sensors was carefully studied. In comparison with SWCNT-based and screen-printed carbon electrodes, CNC/SW sensors showed superior electroanalytical performance in terms of sensitivity and selectivity, not only in the detection of small metabolites (uric acid, dopamine, and tyrosine) but also in the detection of complex glycoproteins (alpha-1-acid glycoprotein (AGP)). More importantly, CNC-II/SW exhibited 20 times higher sensitivity than CNC-I/SW for AGP determination, yielding a LOD of 7 mg L^-1.These results demonstrate the critical role played by nanocellulose polymorphism in the electrochemical performance of CNC/SW hybrid materials, opening new directions in the electrochemical sensing of these complex molecules. In general, these high-active-surface hybrids smartly exploited the preserved non-oxidized SW conductivity with the high aqueous dispersibility of the CNC, avoiding the use of organic solvents or the incorporation of toxic surfactants during their processing, making the CNC/SW hybrids promising nanomaterials for electrochemical detection following greener approaches.

Recent advances in microchip enantioseparation and analysis

This review summarizes recent developments (over the past decade) in the field of microfluidics-based solutions for enantiomeric separation and detection. The progress in various formats of microchip electrodriven separations, such as MCE, microchip electrochromatography, and multidimensional separation techniques, is discussed. Innovations covering chiral stationary phases, surface coatings, and modification strategies to improve resolution, as well as integration with detection systems, are reported. Finally, combinations with other microfluidic functional units are also presented and highlighted.

Carbon nanotubes in microfluidic lab-on-a-chip technology: current trends and future perspectives

Advanced nanomaterials such as carbon nano-tubes (CNTs) display unprecedented properties such as strength, electrical conductance, thermal stability, and intriguing optical properties. These properties of CNT allow construction of small microfluidic devices leading to miniaturization of analyses previously conducted on a laboratory bench. With dimensions of only millimeters to a few square centimeters, these devices are called lab-on-a-chip (LOC). A LOC device requires a multidisciplinary contribution from different fields and offers automation, portability, and high-throughput screening along with a significant reduction in reagent consumption. Today, CNT can play a vital role in many parts of a LOC such as membrane channels, sensors and channel walls. This review paper provides an overview of recent trends in the use of CNT in LOC devices and covers challenges and recent advances in the field. CNTs are also reviewed in terms of synthesis, integration techniques, functionalization and superhydrophobicity. In addition, the toxicity of these nanomaterials is reviewed as a major challenge and recent approaches addressing this issue are discussed.

A highly sensitive and reusable electrochemical mercury biosensor based on tunable vertical single-walled carbon nanotubes and a target recycling strategy

Conformational regulation of SAMs was proposed for controlled growth of v-SWCNTs, which were employed to construct a high-performance mercury biosensor using a target recycling strategy.

Low cost microfluidic device based on cotton threads for electroanalytical application

Microfluidic devices are an interesting alternative for performing analytical assays, due to the speed of analyses, reduced sample, reagent and solvent consumption and less waste generation. However, the high manufacturing costs still prevent the massive use of these devices worldwide. Here, we present the construction of a low cost microfluidic thread-based electroanalytical device (μTED), employing extremely cheap materials and a manufacturing process free of equipment. The microfluidic channels were built with cotton threads and the estimated cost per device was only $0.39. The flow of solutions (1.12 μL s(-1)) is generated spontaneously due to the capillary forces, eliminating the use of any pumping system. To demonstrate the analytical performance of the μTED, a simultaneous determination of acetaminophen (ACT) and diclofenac (DCF) was performed by multiple pulse amperometry (MPA). A linear dynamic range (LDR) of 10 to 320 μmol L(-1) for both species, a limit of detection (LOD) and a limit of quantitation (LOQ) of 1.4 and 4.7 μmol L(-1) and 2.5 and 8.3 μmol L(-1) for ACT and DCF, respectively, as well as an analytical frequency of 45 injections per hour were reached. Thus, the proposed device has shown potential to extend the use of microfluidic analytical devices, due to its simplicity, low cost and good analytical performance.

Recent development of carbon electrode materials and their bioanalytical and environmental applications

New synthetic approaches, materials, properties, electroanalytical applications and perspectives of carbon materials are presented.

The Application of Gas Dwell Time Control for Rapid Single Wall Carbon Nanotube Forest Synthesis to Acetylene Feedstock

One aspect of carbon nanotube (CNT) synthesis that remains an obstacle to realize industrial mass production is the growth efficiency. Many approaches have been reported to improve the efficiency, either by lengthening the catalyst lifetime or by increasing the growth rate. We investigated the applicability of dwell time and carbon flux control to optimize yield, growth rate, and catalyst lifetime of water-assisted chemical vapor deposition of single-walled carbon nanotube (SWCNT) forests using acetylene as a carbon feedstock. Our results show that although acetylene is a precursor to CNT synthesis and possesses a high reactivity, the SWCNT forest growth efficiency is highly sensitive to dwell time and carbon flux similar to ethylene. Through a systematic study spanning a wide range of dwell time and carbon flux levels, the relationship of the height, growth rate, and catalyst lifetime is found. Further, for the optimum conditions for 10 min growth, SWCNT forests with ~2500 μm height, ~350 μm/min initial growth rates and extended lifetimes could be achieved by increasing the dwell time to ~5 s, demonstrating the generality of dwell time control to highly reactive gases.

Microchip electrophoresis-single wall carbon nanotube press-transferred electrodes for fast and reliable electrochemical sensing of melatonin and its precursors

In the current work, single-wall carbon nanotube press-transferred electrodes (SW-PTEs) were used for detection of melatonin (MT) and its precursors tryptophan (Trp) and serotonin (5-HT) on microchip electrophoresis (ME). SW-PTEs were simply fabricated by press transferring a filtered dispersion of single-wall carbon nanotubes on a nonconductive PMMA substrate, where single-wall carbon nanotubes act as exclusive transducers. The coupling of ME-SW-PTEs allowed the fast detection of MT, Trp, and 5-HT in less than 150 s with excellent analytical features. It exhibited an impressive antifouling performance with RSD values of ≤2 and ≤4% for migration times and peak heights, respectively (n = 12). In addition, sample analysis was also investigated by analysis of 5-HT, MT, and Trp in commercial samples obtaining excellent quantitative and reproducible recoveries with values of 96.2 ± 1.8%, 101.3 ± 0.2%, and 95.6 ± 1.2% for 5-HT, MT, and Trp, respectively. The current novel application reveals the analytical power of the press-transfer technology where the fast and reliable determination of MT and its precursors were performed directly on the nanoscale carbon nanotube detectors without the help of any other electrochemical transducer.

Quantitative assessment of the effect of purity on the properties of single wall carbon nanotubes

We quantitatively demonstrate the importance of high purity for the application of single wall carbon nanotubes (SWCNTs), materials solely composed of one surface, by examining the effects of carbon impurities on the electrical, thermal, and mechanical properties of both as-grown SWCNT forests and processed buckypaper. While decreases in properties were expected, our results showed the extreme sensitivity of SWCNT properties to carbonaceous impurities either through scattering in the individual SWCNTs or an inhibition of the ability to form inter-SWCNT junctions. Each property showed a nonlinear decrease (as high as 40%) with the addition of low levels of carbon impurities (∼15 wt%), which demonstrates that purity is as important as the crystalline structure.

Lights and shadows on food microfluidics

These insights attempt to share with the community the lights and shadows of one emerging and exciting topic, Food Microfluidics, defined as microfluidic technology for food analysis and diagnosis in important areas such as food safety and quality. The reader is invited to question non-easy interrogations such as why Food Microfluidics, what is the next step and what could we do with the available technology. This article invites food analysts to be seduced by this technology and then to take an interesting trip departing from the main gained achievements, having a look at the crossing bridges over Food Microfluidic challenges or having a look at available technology to start. Finally, this trip arrives at a privileged place to gaze the horizons. A wonderful landscape--full of inspiration--for Food Microfluidics is anticipated. These insights have also been written wishing to give improved conceptual and realistic solutions for food analysis, with the additional hope to attract the community with exciting technology, in order to get novel and unexpected achievements in this field.

A rapid and sensitive method for hydroxyl radical detection on a microfluidic chip using an N-doped porous carbon nanofiber modified pencil graphite electrode

Hydroxyl radicals (˙OH) play an important role in human diseases. Traditional detection methods are time consuming and require expensive instruments. Here, we present a simple and sensitive method for the detection of hydroxyl radicals on a microfluidic chip using an electrochemical technique. Aniline monomer is electrochemically polymerized on the surface of a pencil graphite electrode and carbonized at 800 °C. The resulting N-doped porous carbon nanofiber-modified pencil graphite electrode is embedded into a microfluidic chip directly as a working electrode. 4-Hydroxybenzoic acid (4-HBA) is selected as the trapping agent owing to its unique 3,4-DHBA product and high trapping efficiency. A low detection limit of 1.0 × 10(-6) M is achieved on the microfluidic chip. As a demonstration, the microfluidic chip is successfully utilized for the detection of ˙OH in cigarette smoke. The strong π-π stacking and hydrophobic interactions between the nitrogen-doped carbon materials and the pencil graphite make the modified electrode well-suited for the microfluidic chip.

Surface modified multifunctional nanomedicines for simultaneous imaging and therapy of cancer

INTRODUCTION

To date, a growing number of advanced anticancer nanomedicines (e.g., Doxil(®), Lipoxal(®), DepoCyte(®)) have entered into different phases of clinical trials. However, most of these medicaments fail to differentiate between diseased and normal cells. They also do not have capability of real time monitoring of disease status trough on-demand imaging/sensing of target molecule(s). Multifunctional nanomedicines and theranostics can resolve such limitations, while formulation of these advanced seamless systems appear to involve various sophisticated process, exploiting several bioconjugations.

METHODS

Recent works upon multifunctional nanomedicines for simultaneous imaging and therapy of cancer have been systematically reviewed, focusing on surface modification and application of advanced nanobiomaterials.

RESULTS

Ultimate therapy of malignancies, as complex systems, demands implementation of seamless nanosystems (NSs) that can specifically target the cancerous cells and smartly deliver the anticancer agent(s) into the desired target site. Engineering of such NSs requires in-situ coordination of various technologies (e.g., synthesis, surface modification and bioconjugation) in order to achieve improved pharmacokinetics and pharmacodynamics outcomes.

CONCLUSION

Seamless multimodal NSs have potential to simultaneously target and monitor the tumor cells through homing and imaging/sensing devices and deliver the therapeutic agents. However, to achieve superior pharmacokinetics with maximal efficacy and minimal side effects, these advanced NSs need to become much more intelligent to sense the disease condition and liberate therapeutics on demand.

Integration of a graphite/poly(methyl-methacrylate) composite electrode into a poly(methylmethacrylate) substrate for electrochemical detection in microchips

Traditional fabrication methods for polymer microchips, the bonding of two substrates together to form the microchip, can make the integration of carbon electrodes difficult. We have developed a simple and inexpensive method to integrate graphite/PMMA composite electrodes (GPCEs) into a PMMA substrate. These substrates can be bonded to other PMMA layers using a solvent-assisted thermal bonding method. The optimal composition of the GPCEs for electrochemical detection was determined using cyclic voltammetry with dopamine as a test analyte. Using the optimized GPCEs in an all-PMMA flow cell with flow injection analysis, it was possible to detect 50 nM dopamine under the best conditions. These electrodes were also evaluated for the detection of dopamine and catechol following separation by MCE.

Fast and reliable class-selective isoflavone index determination on carbon nanotube press-transferred electrodes using microfluidic chips

Direct microfluidic electrochemical sensing of class-isoflavones in complex soy samples on press-transferred carbon nanotubes.

Microchip electrophoresis-copper nanowires for fast and reliable determination of monossacharides in honey samples

Microchip electrophoresis (ME) with electrochemical detection has been demonstrated to be a powerful tool in food analysis. However, the coupling of ME with electrochemical detection and nanotechnologies is still in its infancy, knowing that nanomaterials can significantly improve the ME analytical performance. This work reports the coupling between ME and copper nanowires (CuNWs) for the selective analysis of monosaccharides in honey samples. Also, in terms of real applicability, the study of analytical reliability of ME is an issue of paramount importance. To this end, a representative group of nine honey samples were analyzed and the results were compared with those previously obtained by HPLC-refractive index. ME-CuNWs approach allowed the separation of glucose and fructose in <250 s under optimized separation (20 mM NaOH + 10 mM H3 BO3 , pH 12; separation voltage + 1000 V) and detection (E = +0.70 V in 20 mM NaOH + 10 mM H3 BO3 , pH 12) conditions. An excellent stability of EOF during sample analysis was achieved with RSDs for migration times <2% and for amperometric currents <9%. The quantitative contents for individual glucose and fructose obtained using ME-CuNWs in comparison with those obtained by HPLC-refractive index were highly in agreement with errors <10% indicating the reliability of the approach. The excellent analytical performance obtained confirms the analytical potency of ME-CuNWs approach, enhancing the maturity of the microchip technology and opening new avenues for future implementation of applications in the field of food analysis.

Purification of carbon nanotubes by high temperature chlorine gas treatment

Carbon nanotubes (CNTs) have a tremendous amount of potential to become useful components for future practical applications that may become a part of everyday life. While the sp(2) carbon itself is a rather chemically inert material, the issue of residual metal nanoparticle catalysts remains a prominent barrier in the utilization of CNTs in many areas due to the strong influence of these metallic impurities on the redox chemistry of biomarkers. Even with a standard purification procedure, CNTs have been shown to still contain residual metal nanoparticle catalysts. As such, presented in this paper is an improved purification technique for treating the CNTs with the highly reactive Cl2 gas at an elevated temperature of 1000 °C for 10 min, which would result in the vaporization of the metallic impurities as MxCly, leading to a large decrease in the amount of metallic nanoparticle impurities within the CNTs. By means of electrochemistry and X-ray fluorescence analysis, we demonstrate that the behaviour of such Cl2 treated CNTs showed a significant shift towards that of high purity CNTs, with a dramatic decrease in the influence of the residual metallic impurities on the electrochemical behaviour of CNTs. Therefore it is suggested that the Cl2 treatment of carbon nanotubes is a highly promising route towards the production of pure CNTs.