Modified Paper Substrate Research Articles

Combining surface-enhanced Raman spectroscopy (SERS) and paper spray mass spectrometry (PS-MS) for illicit drug detection

There is an ongoing effort in the US illicit drug market to make new psychoactive compounds more potent and addictive. Due to continuous chemical modifications, many fentanyl analogs are developed and mixed with more traditional illicit drugs, such as cocaine and heroin. Detecting fentanyl and fentanyl analogs in these illicit drug mixtures has become more crucial because of the increased potency and associated health risks. Most confirmatory procedures require time-consuming and expensive, highly sophisticated laboratory equipment and experimental procedures, which can delay critical information that might save a victim or find a suspect. In this study, we propose miniaturizing and accelerating this process by combining surface-enhanced Raman spectroscopy (SERS) analysis and paper spray mass spectrometry (PS-MS). For this aim, dual-purposed paper substrates were developed through soaking in Au/Ag nanostars suspensions. These novel, in-house prepared paper SERS substrates showed stability for up to four weeks with and without the presence of drug compounds. Fentanyl analogs with similar SERS spectra were differentiated by coupling with PS-MS. The limit of detection (LOD) for fentanyl on the paper substrates is 34 μg/mL and 0.32 μg/mL for SERS and PS-MS, respectively. Fentanyl and fentanyl analogs show selective SERS enhancement that helped to detect trace amounts of these opioids in heroin and cocaine street samples. In short, we propose the combination of SERS/PS-MS by using modified paper substrates to develop cost-effective, sensitive, rapid, portable, reliable, and reproducible methods to detect illicit drugs, especially trace amounts of fentanyl and fentanyl analogs in illicit drug mixtures. The combination of these two category A techniques allows for the identification of illicit drugs according to the SWGDRUG guidelines.

Non-equilibrium potentiometric sensors integrated with metal modified paper-based microfluidic solution sampling substrates for determination of heavy metals in complex environmental samples

Metal modified paper-based substrates were utilized for microfluidic paper-based solution sampling coupled with Pb2+-ion selective electrodes (ISEs) with the aim of controlling the super-Nernstian response which usually occurs when using unmodified paper substrates. Potentiometric responses of Pb2+-ISEs coupled with gold, platinum and palladium coated paper substrates were investigated. Potentiometric response time was found to be predominantly dependent on the thickness of metallic layer deposited at the paper substrates. Paper-based substrates coated on both sides with 38 nm gold layers were found to be the most advantageous in controlling the super-Nernstian response of ISEs at non-equilibrium conditions. Durability studies indicated that the lifetime of Pb2+-ISEs could be doubled when used with paper-based substrates in complex environmental samples with high solid-to-liquid content. Determination of lead in real samples using metal modified paper substrates coupled with Pb2+-ISEs was validated by inductively coupled plasma optical emission spectrometry (ICP-OES). Detailed life cycle assessments were performed for model screen printed potentiometric sensors with and without metal modified paper-based solution sampling substrates. The results confirmed that the use of modified paper substrates demonstrated lower environmental impact per potentiometric measurement of Pb2+-ISE in prepared simulated environmental sample as compared to sensors without the use of paper substrates.

Ion-selective membrane modified microfluidic paper-based solution sampling substrates for potentiometric heavy metal detection.

Paper-based microfluidic solution sampling is a viable option for potentiometric sensors to be used for the determination of analytes in samples with high solid-to-liquid ratios. Unfortunately, heavy metal sensitive electrodes cannot be easily integrated with paper-based solution sampling as heavy metals have strong physicochemical adsorption affinity towards paper substrates. In this work, paper substrates were modified with an ion-selective membrane (ISM) cocktail (used for the preparation of Pb2+-ion-selective electrodes (ISEs)) and coupled with model heavy metal Pb2+-ISEs. It was found that the super-Nernstian response of Pb2+-ISEs was eliminated when 10 to 50 mg ml-1 of the ISM cocktail was used for the modification of paper substrates. The modification of the paper substrates by Pb2+-ISM allowed the elimination of adsorption sites. In addition, it resulted in an improvement of sensor performance in terms of their detection limits to be similar to those for conditioned electrodes in standard beaker-based measurements. It is believed that the elimination of super-Nernstian response of the electrodes and improving the potentiometric responses and detection limits of ISEs were attributed to the compatibility improvement of the paper substrates and Pb2+-ISEs to the same type of ISM.

Simultaneous optimization of paper spray substrates and solvents for hydrophilic and hydrophobic molecules

Paper spray mass spectrometry is an ambient ionization technique capable of the direct ionization of analyte from a bio-fluid spot on a paper substrate. Different solvents and types of paper can have different interactions with the analytes of interest; therefore, they can significantly impact the analyte signal and the assay as a whole. In this study, we examined the effects of substrate-solvent composition on signal intensity, blank signal intensity, and signal-to-blank ratio for a variety of pharmaceutical drugs, illicit drugs, chemical warfare agent (CWA) simulants, and CWA hydrolysis products. The analytes were prepared either neat or spiked into human plasma and deposited on a variety of modified paper substrates. Extraction occurred with a range of different solvents. Optimizing the substrate-solvent combination improved the signal-to-blank ratio for all compounds ranging from 1 to 7,964 factor improvement, with the substrate providing a more impactful improvement. Aprotic solvents, such as tetrahydrofuran and ethyl acetate, tended to produce optimal signal-to-blank ratios, while carbon sputtered and glass fiber substrates were the top paper substrates. The research presented herein illustrates the need for systematic optimization of substrate and spray solvent combinations to achieve the best detection limits for paper spray analysis.

Flexible hydrophobic filter paper-based SERS substrate using silver nanocubes for sensitive and rapid detection of adenine

Flexible paper-based surface enhanced Raman spectroscopy (SERS) substrate has attracted great attention in the sensitive detection of analytes in recent years. However, due to its inherent hydrophilic surface, the nanoparticles will not be concentrated very well on the surface of the paper. This reduces the reproducibility and sensitivity of the paper-based substrate. Herein, we demonstrate flexible hydrophobic paper-based substrate using silver nanocubes loaded on polymethylhydrosiloxane modified filter paper (AgNCs@SiO2/PMHS modified filter paper) to realize high sensitivity and reproducibility. The hydrophobic filter paper was obtained by dip-soaking the filter paper into PMHS solution, resulting in increased contact angle to ~112.5°. The AgNCs@SiO2/PMHS modified paper substrate shows high analytical enhancement factor (AEF) of 6.55 × 106, which is 2.2-fold enhancement compared to AgNCs@SiO2/normal paper substrate, and a low detection limit of 0.1 nM rhodamine 6G and 0.89 nM adenine. The high SERS enhancement factor and sensitivity is attributed to the high hotspots density created in the hydrophobic surface as a result of the excellent uniformity and superior sample collection efficiency compared to the normal filter paper-based substrate. Besides, the substrate shows excellent spot-to-spot and substrate-to-substrate reproducibility, with relative standard deviation (RSD) of 6.05% and 9.22%, respectively. Moreover, the AgNCs@SiO2/PMHS modified filter paper substrate achieved good stability; the Raman signal intensity only drops by 25.88% after 3 months of exposure to air. Therefore, this flexible hydrophobic AgNCs@SiO2/PMHS modified filter paper substrate with low cost fabrication and label-free SERS detection is a promising SERS platform for analytical and biological sensing applications.

Fabrication of a "Selenium Signature" Chemical Probe-Modified Paper Substrate for Simultaneous and Efficient Determination of Biothiols by Paper Spray Mass Spectrometry.

Significant efforts have been made to develop robust and reliable methods for simultaneous biothiols determination in different matrices, but there still exist the problems such as easy oxidation, tedious derivatization, and difficulty in discrimination, which brings unsatisfactory results in their accuracy and fast quantification in biological samples. To overcome these problems, a simultaneous biothiols detection method combining a "selenium signature" chemical probe and paper spray mass spectrometry (PS-MS) was proposed. In the strategy, the modified-paper substrate is used to enhance the analytical performance. Chemical probe Ebselen-NH2 that has a specific response to biothiols was designed and covalently fixed on the surface of an oxidized paper substrate. By the identification of derivatized product with distinctive selenium isotope distribution and employment of the optimized PS-MS method, qualitative and quantitative analysis of five biothiols including glutathione (GSH), cysteine (Cys), cysteinylglycine (CysGly), N-acetylcysteine (Nac), and homocysteine (Hcy) were realized. Biothiols in plasma and cell lysates were measured with satisfactory results. The established method not only provides a novel protocol for simultaneous determination of biothiols, but also is helpful for understanding the biological and clinical roles played by these bioactive small molecules.

The fabrication of paper separation channel based SERS substrate and its recyclable separation and detection of pesticides.

In this article, a modified paper separation channel SERS substrate was fabricated by a pen writing method for the simultaneous separation and detection of thiuram and dimethoate. The hydrophilic channel was fabricated with both sides of hydrophobic barrier by the Alkylketene dimer (AKD) modified paper substrate, of which the flow dynamic was well conformed to the Lucas-Washburn model and could be used to separate pesticides effectively. As modified by Ag nanoparticles (AgNPs) and ZnO nanoparticles (ZnONPs), the hydrophilic channel exhibited high recyclable SERS detection activity and stability. The separation and detection performance with different target proportion, channel width and sample volume were studied in detail, which have significant influence on the diffusion process. Additionally, the Raman detects intensity on the substrate also showed linear relationship from 100 to 1000μg/L. The calculated limit of detects (LODs) under optimal experimental conditions were 54.57 and 19.16μg/L for dimethoate and thiuram, respectively. Due to the loading of ZnONPs, the substrate could be used repeatably with good stability. The convenient preparation, effective separation and repeatability make this paper based separation channel SERS substrate have great potential application on the fast separation and simultaneous detection of various pesticides in complex field.

Production of a NiO/Al primary battery employing powder-based electrodes.

This paper describes the use of aluminum and zinc as anodic materials for a battery employing nickel (II) oxide (NiO) as cathode. Comparison of both materials resulted in the development of a compact, cost effective, and easy to use primary NiO/Al battery employing an alkaline electrolyte. The system features electrodes composed of powder forms of the active materials on modified paper substrates that are contained in a simple multilayer design utilizing thin laminated plastic materials to provide structure and flexibility to the battery as well as a paper separator. Various concentrations of potassium hydroxide (KOH) electrolyte were examined and maximum performance was observed at 6M KOH. A maximum current density and power density of 1.94mA/cm2 and 1mW/cm2 , respectively was achieved. This user-friendly device was able to produce a maximum capacity of 2.33mAh/g when 2mA/g was applied. This work demonstrates the viability of a paper-based battery featuring powder electrodes as a possible power source for microelectronic devices.

Inorganic salt modified paper substrates utilized in paper based microfluidic sampling for potentiometric determination of heavy metals

Inorganic salt modified paper substrates were developed and utilized in microfluidic paper based sampling coupled with potentiometric ion sensors for the determination of heavy metals, such as Cd2+ and Pb2+. The application of paper based sampling without any paper substrate pre-treatment were characterized with super Nernstian response, while the paper substrates with inorganic salt pre-treatment were characterized with standard Nernstian response. The application of inorganic salt modified paper substrates was found advantageous when the cation of the salt in the conditioning solution was the same as the primary cations of the ion-selective electrodes (ISEs). A relatively high concentration of inorganic salts during pre-treatment of the paper substrates, namely Cd(NO3)2 or Pb(NO3)2 with subsequent measurement of cadmium(II) and lead(II), by Cd2+- and Pb2+-ISEs, respectively was needed to sustain Nernstian response of sensors. It was also found that paper substrates facilitate sorption of metal ions onto the paper substrates, with stronger binding strength given to Pb2+ over Cd2+. Moreover, the metal-paper interactions suggest concentration dependent sorption-desorption of metal ion, which can have direct limitations of the use of paper based analytics for the determination of low analyte concentration of heavy metals.

One-step deposition of hydrophobic coatings on paper for printed-electronics applications

The ability to pattern highly conductive features on paper substrates is critically important for applications in radio frequency identification (RFID) tags, displays, sensors, printed electronics, and diagnostics. Ink-jet printing particle-free reactive silver inks is an additive, material efficient and versatile strategy for fabrication of highly conductive patterns; however, the intrinsic wetting properties of cellulose based papers are not suitable to serve as substrates for this process. This study reports one-step and practical modification of the surface of paper substrates using industrially available materials. The paper substrates were dip-coated with films of hydrocarbon and fluorocarbon based polymeric resins. Ink-jet printing particle-free reactive silver inks on the modified paper substrates followed by fast thermal annealing resulted in highly conductive patterns. The coatings improved the conductivity of the patterns and reduced the number of printing layers required to obtain conductivity. We finally demonstrated fabrication of a printed RFID tag on the coated paper substrates operating at the frequency range of 865–870 MHz.

Development of Paper Substrate for Paper Spray Ms in High-Sensitivity Analysis of Biological Samples

Paper spray (PS) has demonstrated a promising future for direct mass spectrometric analysis. In the process of PS, paper substrate has been demonstrated as a crucial factor in determining the final performance of PS-MS, and therefore much attention is paid to modification of paper substrate. In this review, we systematically introduce the development of paper substrate for PS. Various commercial and modified papers are comprehensively reviewed, and much effort is focused on some physical and chemical approaches for modification of paper substrate. The application of modified paper substrates to biological sample analyses is discussed. The future promising directions of paper substrate for PS are highlighted.

New urea-modified paper substrate for enhanced analytical performance of negative ion mode paper spray mass spectrometry

Electrospray ionization mass spectrometry (ESI-MS) analysis in the negative ion mode is adversely affected by ionization suppression caused by electrical discharge and the presence of salts. Paper spray mass spectrometry (PS-MS) also suffers from the above phenomenon, being built on principles similar to those of ESI. Herein, we report the use of a paper substrate modified by 1-[3-(trimethoxysilyl)propyl]urea to improve the sensitivity of quantitative PS-MS analysis in the negative ion mode. The obtained results demonstrated that the urea modified paper substrate can effectively bind anions and highly polar compounds in the sample solution, decreasing competitive ionization in the negative ion mode of PS-MS and significantly reducing the signal intensity of Cl− adducts. In addition, the analyte responses were also significantly improved owing to the decreased electrical discharge observed for the less polar surface to decrease electrical discharge. Compared to non-modified PS-MS, urea-modified PS-MS exhibits a much higher sensitivity, showing 2−109 times improved signal-to-noise ratio (S/N). In real sample analysis, the limits of detection (LODs) of salicylic acid in urine and terpene lactones in Ginkgo biloba extract (EGb) were improved 10-fold and 2–40-fold, respectively, compared to that of non-modified PS-MS.

Preparation of selective conductive copper patterns by pen-on-paper writing combined with electroless plating

Conductive Cu patterns were constructed on flexible paper via selectively electroless plating method, which including multistep procedures, namely, 3-aminopropyltrimethoxysilane (APTMS)-modification, selective Cu0-seeding and Cu-lines deposition. Herein, the Cu0 activation process could be divided into two stages: the Cu2+-absorption in cupric citrate solution and subsequently the Cu2+-reduction using a roller pen filled with sodium borohydride ink. The interaction of APTMS onto paper was confirmed by FT-IR measurement and the results indicated that the –NH2 groups originating from APTMS were grafted on the paper. The elemental analysis of the samples in each step was conducted using XPS measurement. Paper-based conductive patterns were investigated by SEM, XRD and Scotch®-tape test. SEM images illustrated that the Cu lines on the APTMS modified paper substrate was compact and composed of ball-shaped copper nuclei. Moreover, the Cu lines could be selectively plated on the required area of the paper substrate. XRD analysis showed that the obtained Cu patterns had a structure with Cu (1 1 1) preferred orientation, revealing an excellent electromigration resistivity. The resultant Cu patterns exhibited an admired adhesion to modified paper, while the Cu patterns obtained in absence of APTMS modification suffered a failure in the adhesive Scotch®-tape test. The resistivity of copper patterns characterized by the digital four-point probe was 10.3 µΩ cm, which was 6.3 times of the bulk Cu. Meanwhile, paper-based Cu pattern remained excellent conductivity after multifolding. Those results indicated that the method proposed in the present work offered a robust and efficient alternative to manufacture flexible electronics.

Cobalt nano-sheet supported on graphite modified paper as a binder free electrode for peroxide electrooxidation

A novel and binder free Co@graphite/paper electrode is prepared by electrodeposition Co nano-sheet on the surface of a graphite layer modified paper substrate. The morphology and phase structure of the Co@graphite/paper electrode are characterized by scanning electron microscopy equipped with energy dispersive X-ray spectrometer, transmission electron microscope and X-ray diffractometer. The catalytic activity of the Co@graphite/paper electrode for H2O2 electrooxidation is investigated by means of cyclic voltammetry and chronoamperometry. The catalyst combines tightly with the paper and exhibits a good stability. The oxidation current density reaches to 580mAcm−2 in 2mol dm−3 NaOH and 0.5mol dm−3 H2O2 at 0.5V. Besides, we illustrate the reaction mechanization of the H2O2 electrooxidation on the Co film.

Application of functional group modified substrate in room‐temperature phosphorescence, I—β‐cyclodextrin modified paper substrate for enrichment and determination of fluorene and acenaphthene

A novel method for the determination of fluorene and acenaphthene on solid phase extraction-room-temperature phosphorescence (SPE-RTP) was studied. beta-cyclodextrin (beta-CD) was chemically bonded onto chromatography paper by reaction with epichorohydrin in an ultrasonic bath. The RTP signal of fluorene and acenaphthene included on the beta-CD-modified paper was increased more than 10 times compared with non-modified filter paper, indicating the formation of the inclusion complex. The conditions for the of RTP of compounds were studied in detail. The linear ranges of fluorene and acenaphthene concentrations to the RTP intensity were over two orders of magnitude (8.0 x 10(-7)-4.0 x 10(-5) mol/L for fluorene) with a correlation coefficient of 0.999. The concentration limits of detection for fluorene and acenaphthene were 1.11 x 10(-8) mol/L and 3.8 x 10(-7) mo/L, respectively. When the sampling volume was 10 microL, the absolute LODs for fluorene and acenaphthene were 18.4 pg/spot and 0.58 ng/spot, respectively. The modified filter paper was used for solid phase extraction (SPE) and the retention behaviour of fluorene and acenaphthene was examined. The enrichment efficiency of the analytes was higher than 100-fold. The SPE-RTP coupling technique was applied directly to the determination of fluorene and acenaphthnene in environmental water samples.