Highly Stretchable and Compressible Cellulose Ionic Hydrogels for Flexible Strain Sensors.

Stretchable and compressible hydrogels based on natural polymers have received immense considerations for electronics. The feasibility of using pure natural polymer-based hydrogels could be improved if their mechanical behaviors satisfy the requirements of practical applications. Herein, we report highly stretchable (tensile strain ∼126%) and compressible (compression strain ∼80%) cellulose ionic hydrogels (CIHs) among pure natural polymer-based hydrogels including cellulose, chitin, and chitosan via chemical cross-linking based on free radical polymerization of allyl cellulose in NaOH/urea aqueous solution. In addition, the hydrogels have good transparency (transmittance of ∼89% at 550 nm) and ionic conductivity (∼0.16 mS cm-1) and can be worked at -20 °C without freezing and visual loss of transparency. Moreover, the CIHs can serve as reliable and stable strain sensors and have been successfully used to monitor human activities. Significantly, the various properties of hydrogel can be controlled through rationally adjusting the chemically cross-linked density. Our methodology will prove useful in developing the satisfied mechanical and transparent CIHs for a myriad of applications in flexible electronics.

Portable paper sensors for the detection of heavy metals based on light transmission-improved quantification of colorimetric assays.

An accurate quantification method with a wide linearity range is paramount for the development of low-cost, portable and point-of-care sensors. This work reports a new approach to analyze the colorimetric assays on paper-based sensors using the quantification from a light transmission method. Compared to the commonly-developed color intensity measurement on scanned digital images, a portable transmission densitometer is capable of directly quantifying the optical density of colorimetric results. The detection of heavy metals in an aqueous system, including Fe(ii), Cu(ii), and Ni(ii), was carried out to demonstrate the good performance and reliability of this method. Our measurements show that the linear quantification range spans from 0.5-500 mg L-1 for the assays of Cu(ii) and Fe(ii) and from 2-500 mg L-1 for Ni(ii) based on the reading of transmitted light through the assay spot. As a comparison, the linear range is restricted to 0.5-50 mg L-1 for the same assays when analysed by the common reflection method, suggesting a significant improvement in the accuracy and sensitivity of high analyte concentrations from the light transmission method. By expanding the linearity range, this method further streamlines the sampling procedure during analysis and will greatly advance the future development of paper-based analytical sensors.

Barcode-like paper sensor for smartphone diagnostics: an application of blood typing.

This study introduced a barcode-like design into a paper-based blood typing device by integrating with smartphone-based technology. The concept of presenting a paper-based blood typing assay in a barcode-like pattern significantly enhanced the adaptability of the assay to the smartphone technology. The fabrication of this device involved the use of a printing technique to define hydrophilic bar channels which were, respectively, treated with Anti-A, -B, and -D antibodies. These channels were then used to perform blood typing assays by introducing a blood sample. Blood type can be visually identified from eluting lengths in bar channels. A smartphone-based analytical application was designed to read the bar channels, analogous to scanning a barcode, interpret this information, and then report results to users. The proposed paper-based blood typing device is rapidly read by smartphones and easy for the user to operate. We envisage that the adaptation of paper-based devices to the widely accepted smartphone technology will increase the capability of paper-based diagnostics with rapid assay result interpretation, data storage, and transmission.

All-Wood-Based Ionic Power Generator with Dual Functions for Alkaline Wastewater Reuse and Energy Harvesting.

Water-induced electricity harvesting has gained much significance for energy sustainability. Bio-based hydrovoltaic materials increase the attractiveness of this strategy. Although promising, it faces a challenge due to its reliance on fresh water and its inherently low power output. Herein, the energy from alkalinity-gradient power generation demonstrated the feasibility of reuse of alkaline wastewater to develop an all-wood-based water-induced electric generator (WEG) based on ion concentration gradients. The intermittent water droplets bring about uneven distribution of electrolyte and endow delignified wood with the difference of ion concentration along aligned cellulose nanochannels, thus supplying electrical power. The practice of using alkali reservoirs, including industrial wastewater, further contributes to electricity generation. The cubic WEG with a side length of 2 cm can produce an ultrahigh open-circuit voltage of about 1.1 V and a short-circuit current of up to 320 µA. A power output of 6.75 µW cm-2 is correspondingly realized. Series-connected WEGs can be used as an energy source for commercial electronics and self-powered systems. Our design provides a double value proposition, allowing for sustainable energy generation and wastewater reuse.

A novel premixing strategy for highly sensitive detection of nitrite on paper-based analytical devices.

BACKGROUND: Nitrite has been involved in many food processing techniques and its excessive consumption is closely related to the development of different diseases. Therefore, highly sensitive detection of nitrite is significant to ensure food safety. RESULT: This study presents a simple and novel strategy for the highly sensitive detection of nitrite in food using paper-based analytical devices (PADs). In this proposed strategy, the nitrite present in the sample undergoes efficient diazotization when initially mixed with sulfanilamide solution before reacting with N-(1-naphthyl) ethylenediamine dihydrochloride (NED) coated on the detection region of the PAD, leading to the maximum production of colored azo compounds. Specifically, within the concentration range of 0.1-20 mg/L, the LOD and LOQ for the nitrite assay using the premixing strategy are determined as 0.053 mg/L and 0.18 mg/L, respectively which significantly surpass the corresponding values of 0.18 mg/L (LOD) and 0.61 mg/L (LOQ) achieved with the regular Griess reagent analysis. SIGNIFICANCE: The study highlights the critical importance of the premixing strategy in nitrite detection. Under optimized conditions, the strategy demonstrates an excellent limit of detection (LOD) and limit of quantification (LOQ) for nitrite detection in eight different meat samples. In addition to its high precision, the strategy is applicable in the field of nitrite analysis. This strategy could facilitate rapid and cost-effective nitrite analysis in real food samples, ensuring food safety and quality analysis.

Manufacturing biodegradable lignocellulosic films with tunable properties from spent coffee grounds: A sustainable alternative to plastics.

Manufacturing biodegradable lignocellulosic films from spent coffee grounds (SCG) as an alternative to commercial plastics is a viable solution to address plastic pollution. Here, the biodegradable lignocellulosic films from SCG were fabricated via a sequential alkaline treatment and ionic liquid-based dissolution process. The alkaline treatment process could swell the cell wall of SCG, change its carbohydrates and lignin contents, and enhance its solubility in ionic liquids. The prepared SCG films with different lignin contents exhibited outstanding UV blocking capability (42.07-99.99 % for UVB and 20.96-99.99 % for UVA) and light scattering properties, good surface hydrophobicity (water contact angle = 63.2°-88.7°), enhanced water vapor barrier property (2.28-6.79 × 10-12 g/m·s·Pa), and good thermal stability. Moreover, the SCG films exhibit excellent mechanical strength (50.10-81.56 MPa, tensile strength) and biodegradability (fully degraded within 30 days when buried in soil) compared to commercial plastic. The SCG films represent a promising alternative that can replace non-biodegradable plastics.

Making commercial bracelet smarter with a biochemical button module.

Despite the rapid development of mobile health based on wearable devices in recent years, lack of access to biochemical detection remains a vital challenge for most commercial wearable devices, which hinders the provision of effective electronic health records (EHRs) for disease control strategies, and further constraining the development of personalized precision medicine. Herein, we propose a strategy to graft biochemical detection function onto commercial bracelet. Different from the conventional development process of designing a completely new wearable biochemical device, we prefer to upgrade existing commercial wearable device to achieve simpler, faster, and more effective research and commercialization processes. An affordable and user-friendly biochemical button module has been designed that enables to integrate sensitive, specific, and rapid biochemical detection function into the idle space on the strap of the bracelet without increasing the size of the main body. This "Smart Bracelet Plus" shows the ability to simultaneously monitor physical and biochemical signals, and will serve as a reliable and systematic personal diagnostics and monitoring platform for providing real-time EHRs for disease control strategies and improving the efficiency of the healthcare system.

A study of the transport and immobilisation mechanisms of human red blood cells in a paper-based blood typing device using confocal microscopy.

Recent research on the use of bioactive paper for human blood typing has led to the discovery of a new method for identifying the haemagglutination of red blood cells (RBCs). When a blood sample is introduced onto paper treated with the grouping antibodies, RBCs undergo haemagglutination with the corresponding grouping antibodies, forming agglutinated cell aggregates in the paper. A subsequent washing of the paper with saline buffer could not remove these aggregates from the paper; this phenomenon provides a new method for rapid, visual identification of the antibody-specific haemagglutination reactions and thus the determination of the blood type. This study aims to understand the mechanism of RBC immobilization inside the paper which follows haemagglutination reactions. Confocal microscopy is used to observe the morphology of the free and agglutinated RBCs that are labelled with FITC. Chromatographic elution patterns of both agglutinated and non-agglutinated RBCs are studied to gain insight into the transport behaviour of free RBCs and agglutinated aggregates. This work provides new information about RBC haemagglutination inside the fibre network of paper on a microscopic level, which is important for the future design of paper-based blood typing devices with high sensitivity and assaying speed.

Fabrication of biodegradable films with UV-blocking and high-strength properties from spent coffee grounds.

Utilizing spent coffee grounds (SCG) to produce high value-added materials is attractive and meaningful. In this work, a multi-functional biomass film is prepared from SCG and dissolving pulp through a dissolution and regeneration process. Importantly, dissolving pulp as a reinforcing additive can significantly enhance the mechanical strength of the regenerated SCG film. The prepared composite films with SCG contents ranging from 33.33 wt% to 81.82 wt% demonstrate excellent optical and mechanical properties. The composite film with 66.67 wt% SCG exhibits outstanding UV blocking capability (99.43 % for UVB and 96.59 % for UVA) and high haze (69.22%); meanwhile, the composite film with 33.33 wt% SCG performs better mechanical strength (58.69 MPa tensile strength and 3.13 GPa Young's modulus) and superior biodegradability (fully degraded within 26 days by being buried in soil) than commercial plastic. This work generally introduces a facile and practical approach to converting waste SCG into promising materials in various fields.

Development of a pumpless acoustofluidic device for rapid food pathogen detection.

Mixing, homogenization, separation, and filtration are crucial processes in miniaturized analytical systems employed for in-vitro biological, environmental, and food analysis. However, in microfluidic systems achieving homogenization becomes more challenging due to the laminar flow conditions, which lack the turbulent flows typically used for mixing in traditional analytical systems. Here, we introduce an acoustofluidic platform that leverages an acoustic transducer to generate microvortex streaming, enabling effective homogenizing of food samples. To reduce reliance on external equipment, tubing, and pump, which is desirable for Point-of-Need testing, our pumpless platform employs a hydrophilic yarn capable of continuous wicking for sample perfusion. Following the homogenization process, the platform incorporates an array of micropillars for filtering out large particles from the samples. Additionally, the porous structure of the yarn provides a secondary screening mechanism. The resulting system is compact, and reliable, and was successfully applied to the detection of Escherichia coli (E. coli) in two different types of berries using quantitative polymerase chain reaction (qPCR). The platform demonstrated a detection limit of 5 CFU g-1, showcasing its effectiveness in rapid and sensitive pathogen detection.

Mechanisms of red blood cells agglutination in antibody-treated paper.

Recent reports on using bio-active paper and bio-active thread to determine human blood type have shown a tremendous potential of using these low-cost materials to build bio-sensors for blood diagnosis. In this work we focus on understanding the mechanisms of red blood cell agglutination in the antibody-loaded paper. We semi-quantitatively evaluate the percentage of antibody molecules that are adsorbed on cellulose fibres and can potentially immobilize red blood cells on the fibre surface, and the percentage of the molecules that can desorb from the cellulose fibre surface into the blood sample and cause haemagglutination reaction in the bulk of a blood sample. Our results show that 34 to 42% of antibody molecules in the papers treated with commercial blood grouping antibodies can desorb from the fibre surface. When specific antibody molecules are released into the blood sample via desorption, haemagglutination reaction occurs in the blood sample. The reaction bridges the red cells in the blood sample bulk to the layer of red cells immobilized on the fibre surface by the adsorbed antibody molecules. The desorbed antibody also causes agglutinated lumps of red blood cells to form. These lumps cannot pass through the pores of the filter paper. The immobilization and filtration of agglutinated red cells give reproducible identification of positive haemagglutination reaction. Results from this study provide information for designing new bio-active paper-based devices for human blood typing with improved sensitivity and specificity.

Chitin/Ca solvent-based conductive and stretchable organohydrogel with anti-freezing and anti-drying.

Conductive hydrogel flexible sensors have attracted considerable research interest because of their good conductivity, flexibility, and biocompatibility. However, conventional hydrogels suffer from dehydration under ambient environments and freezing at low temperatures. Herein, we prepared a chitin/polyacrylamide organohydrogel with highly stretchable, anti-freezing, and anti-drying properties. This organohydrogel was creatively prepared by one-step radical polymerization in the chitin and calcium chloride/methanol (Ca solvent) aqueous solution. Benefiting from the chitin/Ca solvent system, the organohydrogel shows relatively high stretchability (improve ~5 times), excellent anti-freezing (up to -80 °C) upon long-term storage, and anti-drying (67 days under normal environment) performance. What's more, the reversible noncovalent bonds in the organohydrogel endow it with repeatable multi-purpose adhesion and rapid self-healing, while the abundant free ions grant it good conductivity to be a flexible sensor. Therefore, it is promising that this chitin-based conductive organohydrogel with multifunctionality would provide wide application scopes of flexible electronic devices.

Surface-Enhanced Raman Spectroscopy Substrates for Food Safety and Quality Analysis.

Surface-enhanced Raman spectroscopy (SERS) has been identified as a fundamental surface-sensitive technique that boosts Raman scattering by adsorbing target molecules on specific surfaces. The application of SERS highly relies on the development of smart SERS substrates, and thus the fabrication of SERS substrates has been constantly improved. Herein, we investigate the impacts of different substrates on SERS technology including plasmonic metal nanoparticles, semiconductors, and hybrid systems in quantitative food safety and quality analysis. We first discuss the fundamentals, substrate designs, and applications of SERS. We then provide a critical review of the recent progress of SERS in its usage for screening and detecting chemical and biological contaminants including fungicides, herbicides, insecticides, hazardous colorants, and biohazards in food samples to assess the analytical capabilities of this technology. Finally, we investigate the future trends and provide practical techniques that could be used to fulfill the requirements for rapid analysis of food at a low cost.

3D-printed solar evaporator with seashell ornamentation-inspired structure for zero liquid discharge desalination.

Solar-driven interfacial evaporation has enormous promise for fresh water recovery and salt harvesting, but salt accumulation-related challenges stand in its way. Herein, we report a spined groove-ridge pairs inspired by the shell ornamentation of the Vasticardium vertebratum, which addresses salt accumulation by artfully integrating salt reflux into localized salt crystallization. The seashell-mimetic radial V-groove array enables the 3D evaporator to transport water rapidly and directionally, resulting in high-performance water evaporation (∼95% efficiency) and localized crystallization. The periodic spines enlightened by the spine-bearing ridge on the seashell provide considerable micro-unit salt reflux. The 2-in-1 integration design endows the three-dimensional evaporator with superior solar-driven zero liquid discharge and excellent long-term salt resistance even when dealing with high-salinity brine (20 wt% NaCl) and a series of heavy metallic salt solutions. Our design offers a new alternative solution to avoiding salt scaling and could advance locally crystallized solar evaporators towards practical applications.

Superhydrophilic three-dimensional porous spent coffee ground reduced palladium nanoparticles for efficient catalytic reduction.

The use of functional biodegradable wastes to treat environmental problems would create minimal extra burden to our environment. In this paper, we propose a sustainable and practical strategy to turn spent coffee ground (SCG) into a multifunctional palladium-loaded catalyst for water treatment instead of going into landfill as solid waste. Bleached delignified coffee ground (D-SCG) has a porous structure and a good capability to reduce Pd (II) to Pd (0). A large amount of nanocellulose is formed on the surface of SCG after bleaching by H2O2, which anchors and disperses the palladium nanoparticles (Pd NPs). The D-SCG loaded with Pd NPs (Pd-D-SCG) is superhydrophilic, which facilitates water transport and thus promotes efficient removal of organic pollutants dissolved in water. Pd-D-SCG exhibits excellent room temperature catalytic activity for the removal of 4-nitrophenol (4-NP) and methylene blue (MB) in water and shows good chemical stability and recyclability in water, with no obvious decrease even after five repeated cycles.

Electrogenerated chemiluminescence detection in paper-based microfluidic sensors.

This paper describes the first approach at combining paper microfluidics with electrochemiluminescent (ECL) detection. Inkjet printing is used to produce paper microfluidic substrates which are combined with screen-printed electrodes (SPEs) to create simple, cheap, disposable sensors which can be read without a traditional photodetector. The sensing mechanism is based on the orange luminescence due to the ECL reaction of tris(2,2'-bipyridyl)ruthenium(II) (Ru(bpy)(3)(2+)) with certain analytes. Using a conventional photodetector, 2-(dibutylamino)ethanol (DBAE) and nicotinamide adenine dinucleotide (NADH) could be detected to levels of 0.9 µM and 72 µM, respectively. Significantly, a mobile camera phone can also be used to detect the luminescence from the sensors. By analyzing the red pixel intensity in digital images of the ECL emission, a calibration curve was constructed demonstrating that DBAE could be detected to levels of 250 µM using the phone.

Paper-based analytical device for high-throughput monitoring tetracycline residue in milk.

A low-cost and portable paper-based analytical device has been developed for high throughput and on-site monitoring TC residue in milk through visualized colorimetric reaction. The filtration and concentration effect induced by the porous nature of paper contribute to strengthen the color intensity, leading to quantitative and sensitive detection of tetracycline reaching 1 ppm detection limit, with the linear range of 1-100 ppm both in water and milk samples. The applicability was demonstrated by detection of TC in 18 different types of real milk samples with good recovery ranging from 88% to 113%. Furthermore, the dynamic degradation behavior of tetracycline was monitored through the device. To the best of our knowledge, this is the first report of colorimetric detection of tetracycline in milk using the paper-based device. This simple, fast, cost-effective (~$0.50 per device) and equipment-free paper-based platform provides a promising tool for future application in food and environmental safety.

From brown to colored: Polylactic acid composite with micro/nano-structured white spent coffee grounds for three-dimensional printing.

Functional fillers in three-dimensional (3D) printing composite filaments offer an innovative way spent coffee grounds (SCGs) can be reused. However, the inherent brownness of SCGs places a limit on the color in which the composite filament and, consequently, the finished print appears. Herein, colored composite filaments for fused deposition modeling were successfully fabricated, where micro/nano-structured decolorized SCGs (MN-DSCGs) were embedded within polylactic acid (PLA) matrix. At the optimum condition, the 3D prints using composite filaments exhibit comparable tensile and flexural strength to the PLA counterparts. Also, they demonstrate superior melt flow and excellent print quality. Under the same condition, 3D printed MN-DSCGs/PLA blend has sufficient color restoration as compared to the prints using virgin PLA.

Capillary driven low-cost V-groove microfluidic device with high sample transport efficiency.

In this study we investigate the liquid sample delivery speed and the efficiency of microfluidic channels for low-cost and low-volume diagnostic devices driven only by capillary forces. We select open, non-porous surface grooves with a V-shaped cross section for modeling study and for sensor design. Our experimental data of liquid wicking in V-grooves show an excellent agreement with the theoretical data from the V-groove model of Rye et al. This agreement allows us to quantitatively analyze the liquid wicking speed in V-grooves. This analysis is used to generate data for the design of sensors. By combining V-groove channels and printable paper-like porous detection zones, microfluidic diagnostic sensors can be formed. Non-porous V-grooves can be fabricated easily on polymer film. Suitably long surface V-grooves allow short liquid transport time (<500 ms), thus reducing the evaporation loss of the sample during transport. Non-porous V-grooves also significantly reduce chromatographic loss of the sample during transport, therefore increasing the sample delivering efficiency. Sensors of such design are capable of conducting semi-quantitative chemical and biochemical analysis (i.e. with a calibration curve) with less than 1000 nL of sample and indicator solution in total.

Quantitative biomarker assay with microfluidic paper-based analytical devices.

This article describes the use of microfluidic paper-based analytical devices (muPADs) to perform quantitative chemical assays with internal standards. MicroPADs are well-suited for colorimetric biochemical assays; however, errors can be introduced from the background color of the paper due to batch difference and age, and from color measurement devices. To reduce errors from these sources, a series of standard analyte solutions and the sample solution are assayed on a single device with multiple detection zones simultaneously; an analyte concentration calibration curve can thus be established from the standards. Since the muPAD design allows the colorimetric measurements of the standards and the sample to be conducted simultaneously and under the same condition, errors from the above sources can be minimized. The analytical approach reported in this work shows that muPADs can perform quantitative chemical analysis at very low cost.