Paper-Based Microfluidic Devices by Plasma Treatment

A novel chemiluminescence paper microfluidic biosensor based on enzymatic reaction for uric acid determination

In this work, chemiluminescence (CL) method was combined with microfluidic paper-based analytical device (μPAD) to establish a novel CL μPAD biosensor for the first time. This novel CL μPAD biosensor was based on enzyme reaction which produced H(2)O(2) while decomposing the substrate and the CL reaction between rhodanine derivative and generated H(2)O(2) in acid medium. Microchannels in μPAD were fabricated by cutting method. And the possible CL assay principle of this CL μPAD biosensor was explained. Rhodanine derivative system was used to reach the purpose of high sensitivity and well-defined signal for this CL μPAD biosensor. And the optimum reaction conditions were investigated. The quantitative determination of uric acid could be achieved by this CL μPAD biosensor with accurate and satisfactory result. And this biosensor could provide good reproducible results upon storage at 4°C for at least 10 weeks. The successful integration of μPAD and CL reaction made the final biosensor inexpensive, easy-to-use, low-volume, and portable for uric acid determination, which also greatly reduces the cost and increases the efficiency required for an analysis. We believe this simple, practical CL μPAD biosensor will be of interest for use in areas such as disease diagnosis.

New ionization methods and miniature mass spectrometers for biomedicine: DESI imaging for cancer diagnostics and paper spray ionization for therapeutic drug monitoring

The state-of-the-art in two new ambient ionization methods for mass spectrometry, desorption electrospray ionization (DESI) and paper spray (PS), is described and their utility is illustrated with new studies on tissue imaging and biofluid analysis. DESI is an ambient ionization method that can be performed on untreated histological sections of biological tissue in the open lab environment to image lipids, fatty acids, hormones and other compounds. Paper spray is performed in the open lab too; it involves electrospraying dry blood spots or biofluid deposits from a porous medium. PS is characterized by extreme simplicity and speed: a spot of whole blood or other biofluid is analyzed directly from paper, simply by applying a high voltage to the moist paper. Both methods are being developed for use in diagnostics as a means to inform therapy. DESI imaging is applied to create molecular maps of tissue sections without prior labeling or other sample preparation. Like other methods of mass spectrometry imaging (MSI), it combines the chemical speciation of multiple analytes with information on spatial distributions. DESI imaging provides valuable information which correlates with the disease state of tissue as determined by standard histochemical methods. Positive-ion data are presented which complement previously reported negative-ion data on paired human bladder cancerous and adjacent normal tissue sections from 20 patients. These data add to the evidence already in the literature demonstrating that differences in the distributions of particular lipids contain disease-diagnostic information. Multivariate statistical analysis using principal component analysis (PCA) is used to analyze the imaging MS data, and so confirm differences between the lipid profiles of diseased and healthy tissue types. As more such data is acquired, DESI imaging has the potential to be a diagnostic tool for future cancer detection in situ; this suggests a potential role in guiding therapy in parallel with standard histochemical and immunohistological methods. The PS methodology is aimed at high-throughput clinical measurement of quantitative levels of particular therapeutic agents in blood and other biofluids. The experiment allows individual drugs to be quantified at therapeutic levels and data is presented showing quantitative drug analysis from mixtures of therapeutic drugs in whole blood. Data on cholesterol sulfate, a new possible prostate biomarker seen at elevated levels in diseased prostate tissue, but not in healthy prostate tissue in serum are reported using paper spray ionization.

Electrowetting on paper for electronic paper display

The use of paper as a material for various device applications (such as microfluidics and energy storage) is very attractive given its flexibility, versatility, and low cost. Here we demonstrate that electrowetting (EW) devices can be readily fabricated on paper substrates. Several categories of paper have been investigated for this purpose, with the surface coating, roughness, thickness, and water uptake, among the most important properties. The critical parameter for EW devices is the water contact angle (CA) change with applied voltage. EW devices on paper exhibit characteristics very close to those of conventional EW devices on glass substrates. This includes a large CA change in oil ambient (90-95°), negligible hysteresis (∼2°), and fast switching times of ∼20 ms. These results indicate the promise of low-cost paper-based EW devices for video rate flexible e-paper on paper.

Wax-bonding 3D microfluidic chips

We report a simple, low-cost and detachable microfluidic chip incorporating easily accessible paper, glass slides or other polymer films as the chip materials along with adhesive wax as the recycling bonding material. We use a laser to cut through the paper or film to form patterns and then sandwich the paper and film between glass sheets or polymer membranes. The hot-melt adhesive wax can realize bridge bonding between various materials, for example, paper, polymethylmethacrylate (PMMA) film, glass sheets, or metal plate. The bonding process is reversible and the wax is reusable through a melting and cooling process. With this process, a three-dimensional (3D) microfluidic chip is achievable by vacuating and venting the chip in a hot-water bath. To study the biocompatibility and applicability of the wax-based microfluidic chip, we tested the PCR compatibility with the chip materials first. Then we applied the wax-paper based microfluidic chip to HeLa cell electroporation (EP). Subsequently, a prototype of a 5-layer 3D chip was fabricated by multilayer wax bonding. To check the sealing ability and the durability of the chip, green fluorescence protein (GFP) recombinant Escherichia coli (E. coli) bacteria were cultured, with which the chemotaxis of E. coli was studied in order to determine the influence of antibiotic ciprofloxacin concentration on the E. coli migration.

A simple method of fabricating mask-free microfluidic devices for biological analysis

We report a simple, low-cost, rapid, and mask-free method to fabricate two-dimensional (2D) and three-dimensional (3D) microfluidic chip for biological analysis researches. In this fabrication process, a laser system is used to cut through paper to form intricate patterns and differently configured channels for specific purposes. Bonded with cyanoacrylate-based resin, the prepared paper sheet is sandwiched between glass slides (hydrophilic) or polymer-based plates (hydrophobic) to obtain a multilayer structure. In order to examine the chip's biocompatibility and applicability, protein concentration was measured while DNA capillary electrophoresis was carried out, and both of them show positive results. With the utilization of direct laser cutting and one-step gas-sacrificing techniques, the whole fabrication processes for complicated 2D and 3D microfluidic devices are shorten into several minutes which make it a good alternative of poly(dimethylsiloxane) microfluidic chips used in biological analysis researches.

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.

Paper-based microfluidic devices for analysis of clinically relevant analytes present in urine and saliva

We report the use of paper-based microfluidic devices fabricated from a novel polymer blend for the monitoring of urinary ketones, glucose, and salivary nitrite. Paper-based devices were fabricated via photolithography in less than 3 min and were immediately ready for use for these diagnostically relevant assays. Patterned channels on filter paper as small as 90 microm wide with barriers as narrow as 250 microm could be reliably patterned to permit and block fluid wicking, respectively. Colorimetric assays for ketones and nitrite were adapted from the dipstick format to this paper microfluidic chip for the quantification of acetoacetate in artificial urine, as well as nitrite in artificial saliva. Glucose assays were based on those previously demonstrated (Martinez et al., Angew Chem Int Ed 8:1318-1320, 1; Martinez et al., Anal Chem 10:3699-3707, 2; Martinez et al., Proc Nat Acad Sci USA 50:19606-19611, 3; Lu et al., Electrophoresis 9:1497-1500, 4; Abe et al., Anal Chem 18:6928-6934, 5). Reagents were spotted on the detection pad of the paper device and allowed to dry prior to spotting of samples. The ketone test was a two-step reaction requiring a derivitization step between the sample spotting pad and the detection pad, thus for the first time, confirming the ability of these paper devices to perform online multi-step chemical reactions. Following the spotting of the reagents and sample solution onto the paper device and subsequent drying, color images of the paper chips were recorded using a flatbed scanner, and images were converted to CMYK format in Adobe Photoshop CS4 where the intensity of the color change was quantified using the same software. The limit of detection (LOD) for acetoacetate in artificial urine was 0.5 mM, while the LOD for salivary nitrite was 5 microM, placing both of these analytes within the clinically relevant range for these assays. Calibration curves for urinary ketone (5 to 16 mM) and salivary nitrite (5 to 2,000 microM) were generated. The time of device fabrication to the time of test results was about 25 min.

Diagnostics for the developing world: microfluidic paper-based analytical devices

Microfluidic paper-based analytical devices (microPADs) are a new class of point-of-care diagnostic devices that are inexpensive, easy to use, and designed specifically for use in developing countries. (To listen to a podcast about this feature, please go to the Analytical Chemistry multimedia page at pubs.acs.org/page/ancham/audio/index.html.).

The extraction of liquid, protein molecules and yeast cells from paper through surface acoustic wave atomization

Paper has been proposed as an inexpensive and versatile carrier for microfluidics devices with abilities well beyond simple capillary action for pregnancy tests and the like. Unlike standard microfluidics devices, extracting a fluid from the paper is a challenge and a drawback to its broader use. Here, we extract fluid from narrow paper strips using surface acoustic wave (SAW) irradiation that subsequently atomizes the extracted fluid into a monodisperse aerosol for use in mass spectroscopy, medical diagnostics, and drug delivery applications. Two protein molecules, ovalbumin and bovine serum albumin (BSA), have been preserved in paper and then extracted using atomized mist through SAW excitation; protein electrophoresis shows there is less than 1% degradation of either protein molecule in this process. Finally, a solution of live yeast cells was infused into paper, which was subsequently dried for preservation then remoistened to extract the cells via SAW atomization, yielding live cells at the completion of the process. The successful preservation and extraction of fluids, proteins and yeast cells significantly expands the usefulness of paper in microfluidics.

Thread as a versatile material for low-cost microfluidic diagnostics

This paper describes a new and simple concept for fabricating low-cost, low-volume, easy-to-use microfluidic devices using threads. A thread can transport liquid via capillary wicking without the need of a barrier; as it is stainable, it is also a desirable material for displaying colorimetric results. When used in sewing, threads have 3D passageways in sewed materials. The wicking property and flexibility of thread make it particularly suitable to fabricate 3D microfluidic devices. Threads can also be used with other materials (e.g., paper) to make microfluidic devices for rapid qualitative or semiquantitative analysis. These thread-based and thread-paper-based devices have potential applications in human health diagnostics, environmental monitoring, and food safety analysis, and are particularly appropriate for the developing world or remote areas, because of their relatively low fabrication costs.

Patterning of superhydrophobic paper to control the mobility of micro-liter drops for two-dimensional lab-on-paper applications

Superhydrophobic paper substrates were patterned with high surface energy black ink using commercially available desktop printing technology. The shape and size of the ink islands were designed to control the adhesion forces on water drops in two directions, parallel ('drag-adhesion') and perpendicular ('extensional-adhesion') to the substrate. Experimental data on the adhesion forces shows good agreement with classical models for 'drag' (Furmidge equation) and 'extensional' adhesion (modified Dupré equation). The tunability of the two adhesion forces was used to implement four basic unit operations for the manipulation of liquid drops on the paper substrates: storage, transfer, mixing and sampling. By combining these basic functionalities it is possible to design simple two-dimensional lab-on-paper (LOP) devices. In our 2D LOP prototype, liquid droplets adhere to the porous substrate, rather than absorbing into the paper; as a result, liquid droplets remain accessible for further quantitative testing and analysis, after performing simple qualitative on-chip testing. In addition, the use of commercially available desktop printers and word processing software to generate ink patterns enable end users to design LOP devices for specific applications.

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.

Multivalent anchoring and oriented display of single-domain antibodies on cellulose

Antibody engineering has allowed for the rapid generation of binding agents against virtually any antigen of interest, predominantly for therapeutic applications. Considerably less attention has been given to the development of diagnostic reagents and biosensors using engineered antibodies. Recently, we produced a novel pentavalent bispecific antibody (i.e., decabody) by pentamerizing two single-domain antibodies (sdAbs) through the verotoxin B subunit (VTB) and found both fusion partners to be functional. Using a similar approach, we have engineered a bispecific pentameric fusion protein consisting of five sdAbs and five cellulose-binding modules (CBMs) linked via VTB. To find an optimal design format, we constructed six bispecific pentamers consisting of three different CBMs, fused to the Staphylococcus aureus-specific human sdAb HVHP428, in both orientations. One bispecific pentamer, containing an N-terminal CBM9 and C-terminal HVHP428, was soluble, non-aggregating, and did not degrade upon storage at 4 °C for over six months. This molecule was dually functional as it bound to cellulose-based filters as well as S. aureus cells. When impregnated in cellulose filters, the bispecific pentamer recognized S. aureus cells in a flow-through detection assay. The ability of pentamerized CBMs to bind cellulose may form the basis of an immobilization platform for multivalent display of high-avidity binding reagents on cellulosic filters for sensing of pathogens, biomarkers and environmental pollutants.