Gold nanoparticle-functionalized thread as a substrate for SERS study of analytes both bound and unbound to gold

The onset of surface-enhanced Raman scattering for single-particle detection of submicroplastics

Microplastics represent an emerging environmental problem worldwide, raising ecological and food safety concerns. Compared to microplastics, there is growing evidence of an even higher abundance of submicro- and nanoplastics in the environment, but a reliable monitoring method for detecting these smaller-sized plastics is lacking. Herein we presented the application of surface-enhanced Raman scattering (SERS) for this purpose. Particles of polystyrene (PS; 600 nm) were used as the probe analyte. Gold nanourchins (AuNU; 50 nm), i.e. urchin-shaped nanoparticles with irregular spikes around the core, were used as the SERS-active substrate. The effectiveness of SERS on PS was evaluated at a single-particle level with different numbers of AuNU in order to determine the minimum conditions required for the onset of the SERS effect. Our findings suggest that SERS of a single particle of PS can be induced by as few as 1-5 particles of AuNU, and that the use of excitation wavelength at 785 nm is appropriate to meet the red-shifted surface plasmon resonance of AuNU upon aggregation. These specifications provide additional information for the development of SERS-based tools for detecting plastic particles < 1 µm in food and environmental samples.

Gold Nanoparticles Synthesis and Antimicrobial Effect on Fibrous Materials

Depositing nanoparticles in textiles have been a promising strategy to achieve multifunctional materials. Particularly, antimicrobial properties are highly valuable due to the emergence of new pathogens and the spread of existing ones. Several methods have been used to functionalize textile materials with gold nanoparticles (AuNPs). Therefore, this review highlighted the most used methods for AuNPs preparation and the current studies on the topic in order to obtain AuNPs with suitable properties for antimicrobial applications and minimize the environmental concerns in their production. Reporting the detailed information on the functionalization of fabrics, yarns, and fibers with AuNPs by different methods to improve the antimicrobial properties was the central objective. The studies combining AuNPs and textile materials have opened valuable opportunities to develop antimicrobial materials for health and hygiene products, as infection control and barrier material, with improved properties. Future studies are needed to amplify the antimicrobial effect of AuNPs onto textiles and minimize the concerns related to the synthesis.

Low-Cost Synthesis of Gold Nanoparticles from Reused Traditional Gold Leaf and its Application for Sensitive and Selective Colorimetric Sensing of Creatinine in Urine

Background:

Gold nanoparticles (Au NPs) are normally prepared using standard gold (III) trichloride which is much expensive and irritant. This work is aimed at demonstrating simple and low-cost synthesis of Au NPs from the reused traditional gold leaf which is cost-free and less toxic.

Methods:

The reused gold leaf was donated by the local temple. It was digested and used as the precursor for the preparation of the Au NPs by Turkevich method. Poly (vinyl alcohol) (PVA) was employed as a stabilizer. The as-prepared Au NPs were applied for the colorimetric determination of creatinine in urine without any sample pretreatment.

Results:

Long-term stability of the gold colloids was achieved for at least 3 months. Morphology and purity of the as-prepared Au NPs were the same as the ones prepared from standard gold (III) salt and standard gold foil. Colorimetric response of the Au NPs was linear to the standard creatinine up to 200 mg L-1. The limit of detection (0.16 mg L-1 or 1.41 μM) was enough sensitive for urinary creatinine detection in patients with kidney disease. Good recoveries (97-108%) and fast analysis time (3 min) were achieved. The developed method was successfully validated against the HPLC method.

Conclusion:

Facile and cost-effective synthesis of the Au NPs from the reused traditional gold leaf, was accomplished. The as-prepared Au NPs were successfully applied for the determination of urinary creatinine with high sensitivity and selectivity.

Life-Saving Threads: Advances in Textile-Based Analytical Devices

Novel approaches that incorporate electrofluidic and microfluidic technologies are reviewed to illustrate the translation of traditional enclosed structures into open and accessible textile based platforms. Through the utilization of on-fiber and on-textile microfluidics, it is possible to invert the typical enclosed capillary column or microfluidic "chip" platform, to achieve surface accessible efficient separations and fluid handling, while maintaining a microfluidic environment. The open fiber/textile based fluidics approach immediately provides new possibilities to interrogate, manipulate, redirect, extract, characterize, and quantify solutes and target species at any point in time during such processes as on-fiber electrodriven separations. This approach is revolutionary in its simplicity and provides many potential advantages not otherwise afforded by the more traditional enclosed platforms.

Fibre-based electrofluidics on low cost versatile 3D printed platforms for solute delivery, separations and diagnostics; from small molecules to intact cells

A novel and effective fibre-based microfluidic methodology was developed to move and isolate charged solutes, biomolecules, and intact bacterial cells, based upon a novel multi-functional 3D printed supporting platform, with potential applications in the fields of microfluidics and biodiagnostics. Various on-fibre electrophoretic techniques are demonstrated to separate, pre-concentrate, move, split, or cut and collect the isolated zones of target solutes, including proteins and live bacterial cells. The use of knotting to link different fibre materials, and the unique ability of this approach to physically concentrate solutes in different locations are shown such that the concentrated solutes can be physically isolated and easily transferred to other fibres. Application of this novel fibre-based technique within a potential diagnostic platform for urinary tract infection is shown, together with the post-electrophoretic incubation of live bacterial cells, demonstrating the cell survival following on-fibre electrophoretic concentration.

Trace Analysis and Chemical Identification on Cellulose Nanofibers-Textured SERS Substrates Using the "Coffee Ring" Effect

Surface-enhanced Raman scattering (SERS) has the theoretical possibility of detecting chemicals at the single molecular level. This potential is frequently limited, however, by the critical requirements of the surface morphology and mechanical stability of SERS substrates. In this paper, we report a new method for fabricating a SERS substrate with a significantly improved mechanical stability and analytical sensitivity, using cellulose nanofibers (CNFs) and gold nanoparticles (AuNPs). We constructed a uniformly CNFs-textured substrate on a glass surface by means of suppressing the "coffee ring" effect of the CNF sessile drop and then introduced an AuNP suspension onto the CNFs-textured substrate by taking advantage of the "coffee ring" effect. A widened detection zone is formed by AuNPs on the CNFs-textured glass, producing a stable SERS substrate for trace analysis and chemical identification. Microscopic and spectroscopic characterizations of the CNF-AuNPs SERS substrate show that the CNFs enhance the stability of both the AuNP clusters and the SERS activity. The CNF-AuNPs SERS substrate is significantly more stable and sensitive than the SERS substrate fabricated by directly depositing the AuNP suspension on a smooth glass surface.

A biomolecular recognition approach for the functionalization of cellulose with gold nanoparticles

Materials with new and improved functionalities can be obtained by modifying cellulose with gold nanoparticles (AuNPs) via the in situ reduction of a gold precursor or the deposition or covalent immobilization of pre-synthesized AuNPs. Here, we present an alternative biomolecular recognition approach to functionalize cellulose with biotin-AuNPs that relies on a complex of 2 recognition elements: a ZZ-CBM3 fusion that combines a carbohydrate-binding module (CBM) with the ZZ fragment of the staphylococcal protein A and an anti-biotin antibody. Paper and cellulose microparticles with AuNPs immobilized via the ZZ-CBM3:anti-biotin IgG supramolecular complex displayed an intense red color, whereas essentially no color was detected when AuNPs were deposited over the unmodified materials. Scanning electron microscopy analysis revealed a homogeneous distribution of AuNPs when immobilized via ZZ-CBM3:anti-biotin IgG complexes and aggregation of AuNPs when deposited over paper, suggesting that color differences are due to interparticle plasmon coupling effects. The approach could be used to functionalize paper substrates and cellulose nanocrystals with AuNPs. More important, however, is the fact that the occurrence of a biomolecular recognition event between the CBM-immobilized antibody and its specific, AuNP-conjugated antigen is signaled by red color. This opens up the way for the development of simple and straightforward paper/cellulose-based tests where detection of a target analyte can be made by direct use of color signaling.

Low-cost, high-throughput fabrication of cloth-based microfluidic devices using a photolithographical patterning technique

In this work, we first report a facile, low-cost and high-throughput method for photolithographical fabrication of microfluidic cloth-based analytical devices (μCADs) by simply using a cotton cloth as a substrate material and employing an inexpensive hydrophobic photoresist laboratory-formulated from commercially available reagents, which allows patterning of reproducible hydrophilic-hydrophobic features in the cloth with well-defined and uniform boundaries. Firstly, we evaluated the wicking properties of cotton cloths by testing the wicking rate in the cloth channel, in combination with scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analyses. It is demonstrated that the wicking properties of the cloth microfluidic channel can be improved by soaking the cloth substrate in 20 wt% NaOH solution and by washing the cloth-based microfluidic patterns with 3 wt% SDS solution. Next, we studied the minimum dimensions achievable for the width of the hydrophobic barriers and hydrophilic channels. The results indicate that the smallest width for a desired hydrophobic barrier is designed to be 100 μm and that for a desired hydrophilic channel is designed to be 500 μm. Finally, the high-throughput μCADs prepared using the developed fabrication technique were demonstrated for colorimetric assays of glucose and protein in artificial urine samples. It has been shown that the photolithographically patterned μCADs have potential for a simple, quantitative colorimetric urine test. The combination of cheap cloth and inexpensive high-throughput photolithography enables the development of new types of low-cost cloth-based microfluidic devices, such as "microzone plates" and "gate arrays", which provide new methods to perform biochemical assays or control fluid flow.

The development of “fab-chips” as low-cost, sensitive surface-enhanced Raman spectroscopy (SERS) substrates for analytical applications

Modification of metal-coated zari fabric chips with silver nanoparticles results in sensitive, affordable SERS substrates which are useful for a wide range of chemical sensing applications.