WO2020093379A1

WO2020093379A1 - Nanofibrillated-cellulose-paper-based microfluidic devices

Info

Publication number: WO2020093379A1
Application number: PCT/CN2018/114863
Authority: WO
Inventors: Binbin Ying; Xinyu Liu
Original assignee: Jiangsu Jitri Micro-Nano Automation Institute Co Ltd
Current assignee: Jiangsu Jitri Micro-Nano Automation Institute Co Ltd
Priority date: 2018-11-09
Filing date: 2018-11-09
Publication date: 2020-05-14
Anticipated expiration: 2021-05-09
Also published as: CN113226551A

Abstract

A nanofibrillated-cellulose-paper-based microfluidic device comprising a transparent hollow channel fluidly connecting a fluid inlet to a fluid outlet, the transparent hollow channel comprise a fluid flow path defined by a floor, two or more side walls, and a ceiling, the floor comprises a transparent nanofibrillated cellulose paper, and the ceiling comprises a transparent NFC paper. The device is pump-free and broadening the application of paper-based microfluidics.

Description

Nanofibrillated-Cellulose-Paper-Based Microfluidic Devices

FIELD OF THE INVENTION

The present invention relates to the field of microfluidic devices for detection of analyte in a fluid, and more particularly to a pump-free, transparent paper-based microfluidic device.

BACKGROUND OF THE INVENTION

Here nanofibrillated cellulose (NFC) paper (or simply nanopaper) was used as substrates to simply fabricate highly transparent hollow-channel nanopaper-based analytical devices (nanoPAD) . Two rapid detection devices based on this design were developed: one for surface enhance Raman scattering (SERS) detection, and another for colorimetric detection.

Paper has been widely used as the material of microfluidic analytical devices since the Whitesides group firstly reported a photolithography patterned paper-based platform for conducting multiplexed bioassays. Compared with polydimethylsiloxane (PDMS) or plastic based microfluidics devices, paper-based microfluidics is of low cost, technically simple, and biodegradable. Another feature of paper is its hydrophilicity that makes paper-based analytical devices pump-free. However, there are some limitations using paper as an analytical platform: slow liquid flow speed in normal porous paper channels induces the issue of serious solvent evaporation; porous cellulose structure induces nonspecific adsorption and hinders free movement of micrometer-sized objects within paper matrix. Lately, the Whitesides group demonstrated an open-channel microfluidic device by craft-cut a trench on thick omniphobic paper to remove the paper matrix (PCT patent application No. : PCT/US2014/018680) . In another demonstration, hollow-channel based microfluidic paper analytical device, was reported to enable rapid fluid flow with no requirement of a pump (US patent application No: US20170173578A1) . The flow speed in hollow channels is 7 times higher than that in porous paper channels. Simple colorimetric assays and electrochemical detection have been developed base on this design.

However, regular paper is usually not optically transparent, and this problem limits some microfluidic applications (e.g. absorption spectroscopy, fluorescence or electrochemiluminescence -ECL) that require light transmission and/or light emission. The Whitesides group described the use of transparent cellophane coated with a thick layer of nitrocellulose to fabricate an open-channel microfluidic device (PCT patent application No. PCT/US2017/051533) . Specifically, they embossed channel on one layer of coated cellophane and heat-sealed the embossed one with another layer of coated cellophane. Laminar flow was observed in this sort of open-channel microfluidics device, and some basic microfluidic operations like generation of droplets and slugs in multiphase flow and mixing were demonstrated. ECL detection was also shown through printing electrodes on the surface of the coated cellophane and embedding into layered microfluidics platforms. However, these coated open-channels are hydrophobic, therefore, a syringe pump is necessary for forming a fluidic flow.

Recently, a new cellulose material, NFC, has been developed to fabricate highly transparent paper. NFC paper has been used as the template of a plasmonic and photoluminescent optical sensing platform. Like regular paper, NFC paper is hydrophilic (its contact angle is around 30°) , biodegradable, flexible and of low cost. Another feature of the NFC paper film is its pores size at the nanoscale (10-50 nm) , and its extremely smooth surface; thus, this material has been widely used as substrates of electronics. This invention demonstrates the utilization of the NFC paper for constructing transparent paper-based microfluidic devices.

SUMMARY OF INVENTION

In order to solve the aforementioned technical problems of paper-based microfluidic devices, the invention provides a pump-free, transparent Nanofibrillated-cellulose-paper-based microfluidic device, and the device uses NFC paper as the device substrate, and adopts the hollow-channel architecture for pump-free fluid transfer.

For the above purpose, the invention utilizes the following technical solutions.

In one aspect, the invention provides a pump-free, transparent paper-based microfluidic device and the device a transparent hollow channel fluidly connecting a fluid inlet to a fluid outlet. The transparent hollow channel comprises a fluid flow path defined by a floor, two or more side walls, and a ceiling. The floor comprises a transparent nanofibrillated cellulose (NFC) paper, and the ceiling comprises a transparent NFC paper.

Preferably, the floor of the hollow channel comprises transparent hydrophilic NFC paper.

Preferably, the ceiling of the hollow channel comprises transparent hydrophilic NFC paper.

Preferably, the side walls of the hollow channel comprise a hydrophobic material.

Preferably, the side walls of the hollow channel are selected from the group consisting of a hydrophobic material, a hydrophilic material, and any combinations thereof.

Preferably, the hydrophobic material comprises a paper covalently modified to comprise a hydrophobic agent, paper impregnated with a hydrophobic agent, a paper coated with a hydrophobic agent, or any combinations thereof.

Preferably, the hydrophilic material is selected from the group consisting of NFC paper, microfibrillated cellulose (MFC) paper, bacterial nanocellulose paper, and any combinations thereof.

More preferably, the hollow channel transports a fluid without an external pressure applied to the inlet or outlet of the device.

Preferably, the device further comprises an assay reagent in contact with the hollow channel.

Preferably, the device further comprises a surface enhanced Raman scattering (SERS) substrate material in contact with the hollow channel.

Preferably, the SERS substrate material selected from the group consisting of gold nanostructures, silver nanostructures, nanostructures of any other materials with surface Raman enhancement effect, and any combinations thereof.

Preferably, the device further comprises a detection device configured to measure an optical signal inside the hollow channel.

Preferably, the detection device comprises a camera, a cell phone, a fluorescence meter, a spectrometer, or any combinations thereof.

In another aspect, the invention provides a method of fabricating a paper-based microfluidic device comprising steps of:

providing a first paper sheet, a second paper sheet, a third paper sheet, and a bonding material,

cutting one or more openings on the first paper sheet or the third paper sheet to form a fluid inlet or outlet of the device,

cutting one or more openings on the second paper sheet to form the microfluidic channel patterns,

bonding the first paper sheet and the second paper sheet together using the bonding material, and

bonding the third paper sheet onto the second paper sheet side of the bonded bilayer of the first and second paper sheets using the bonding material.

Preferably, the first paper sheet and the third paper sheet respectively are selected from the group consisting of NFC paper, MFC paper, bacterial nanocellulose paper, and any combinations thereof.

Preferably, the bonding material is selected from the group consisting of ethylene vinyl acetate, glue, double-sided adhesive tape, and any combinations thereof.

Preferably, the cutting of the paper sheets is selected from laser cutting, blade cutting, or a combination thereof.

Preferably, the bonding of paper sheets is selected from mechanical compressing, thermal compressing, and a combination thereof.

In a further aspect, the invention also provides a method of fabricating a paper-based microfluidic device comprising steps of:

cutting one or more openings on the first paper sheet or the third paper sheet to form the fluid inlet or outlet of the device,

bonding the first paper sheet and the second paper sheet together using the bonding material,

coating the microfluidic channel area of the first paper sheet with a SERS substrate material, and

Preferably, the first paper sheet and the third paper sheet are respectively selected from the group consisting of NFC paper, MFC paper, bacterial nanocellulose paper, and any combinations thereof.

Preferably, the bonding material is selected from the group consisting of ethylene vinyl acetate, glue, double-sided adhesive tape, or any combinations thereof.

Preferably, the bonding material can be a glue, a transparent double tape, or a combination thereof.

Preferably, the SERS substrate material is selected from the group consisting of gold nanostructures, silver nanostructures, nanostructures of any other materials with surface Raman enhancement effect, and any combinations thereof.

Preferably, the cutting of the paper sheets is laser cutting, blade cutting, or a combination thereof. Preferably, the bonding of paper sheets is mechanical compressing, thermal compressing, and a combination thereof.

Preferably, the coating of the SERS substrate material is selected from the group consisting of casting and then drying of a solution of pre-synthesized SERS substrate material, in-situ synthesis of SERS substrate material, or a combination thereof.

By means of the above technical solutions, as compared with the prior art, the invention has the following advantages: the invention provides a paper-based microfluidic device including one or more transparent hollow-channel fluidly connecting a fluid inlet to a fluid outlet. In the invention, NFC paper was the first time used as the substrate of paper-based hollow-channel microfluidics, and a novel highly transparent hollow-channel paper device was easily obtained, thereby broadening the application of paper-based microfluidics.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the NFC paper and its characterization: (a) transmission electron microscopy (TEM) photograph of cellulose nanofiber (the scale bar : 100 nm; (b) photograph of a 80 um-thick NFC paper; (c) the transmittance of NFC paper in Fig. 1b; (d) atomic force microscopy (AFM) surface roughness over a 1 um x 1 um of NFC paper area.

FIG. 2 shows design and characterization of the transparent hollow-channel nanoPAD: (a) schematic view of a hollow-channel nanoPAD; (b) photograph of a nanoPAD with 3 channels; (c) characterization of vertical wicking speed along a 2-mm-width channel; (d) characterization of vertical wicking speed among channels with widths of 1, 2 and 3 mm when fluid height is 10 mm.

FIG. 3 shows SERS spectra of rhodamine B (RhB) with different concentrations on the hollow-channel nanoPAD SERS platform: (a) experimental results of Raman spectrum when increasing the RhB concentration from 0.1 uM to 1000 uM in hollow channels; (b) the calibration curve obtained from the change in SERS signal around 1650 cm ^-1 measured from (a) .

FIG. 4: (a) photograph of the hollow channels after 10 min colorimetric reaction; (b) experimental results of color intensities with glucose concentration of 4, 8, 12, 16 and 20 mM (N=5) .

FIG. 5 shows characterization of Au nanostars suspension: (a) TEM images of branched Au NSs at the scale bar of 100 nm and the inset includes Au nanostar at the scale bar of 20 nm; (b) UV-vis spectrum of branched Au NSs. The inset shows a digital picture of the aqueous solution of branched Au NSs.

DETAILED DESCRIPTION OF THE INVENTION

The invention will be further illustrated in more detail with reference to the accompanying drawings and embodiments. It is noted that, the following embodiments only are intended for purposes of illustration, but are not intended to limit the scope of the present invention.

Experimental Methods:

Reagents and Materials: (2, 2, 6, 6-tetramethylpiperidin-1-yl) oxidanyl (TEMPO) -Cellulose Nanofibrils (slurry, 0.3-1.0%solids) was supplied by the Process Development Center of University of Maine. ethylene vinyl acetate (EVA) film was obtained from Tianjin Caida New Materials Technology Co., Ltd. (Tianjin, China) . Gold (III) chloride trihydrate (HAuCl ₄, >99%) , Rhodamine B (RhB, >95%) , 4- (2-Hydroxyethyl) piperazine-1-ethanesulfonic acid, N- (2-Hydroxyethyl) piperazine-N’- (2-ethanesulfonic acid) (HEPES, >99.5%) and phosphate buffered saline solution (PBS, 10×) were purchased from Sigma-Aldrich (St. Louis, MO, USA) . The solutions were diluted by deionized water (18.2 MΩ·cm, Milli-Q Gradient System, Millipore) . All the reagents employed in this colorimetric test were purchased from Sigma-Aldrich Canada. Biomarker analytes in the colorimetric test was d- (+) -glucose (99.5 %) . Accordingly, oxidation enzyme solution was mixed using 120 UmL ^-1 glucose oxidase (from Aspergillus niger, 147, 900 units/g) and 30 UmL ^-1 peroxidase type I (from horseradish, 50 units/mg) . 0.3 M Trehalose was used as stabilizer. Oxidation indicator was mixed using 0.2 M 4-aminoantipyrine and 0.4 M 3, 5-dichloro-2-hydroxy-benzenesulfonic acid. The preparation of artificial urine solution was reported previously. The artificial urine solution contained 2.5 mM calcium chloride, 2 mM citric acid, 90 mM sodium chloride, 1.1 mM lactic acid, 2 mM magnesium sulfate, 10 mM sodium sulfate, 7 mM potassium dihydrogen phosphate, 170 mM urea, 25 mM sodium bicarbonate, 7 mM dipotassium hydrogen phosphate, and 25 mM ammonium chloride. The pH of the solution was adjusted to 6 by adding 1 M hydrochloric acid.

Film Made from

polytetrafluoroethylene (PTFE) film and polyethylene terephthalate (PET) film were ordered from McMaster-CARR.

NFC Paper Preparation: In a typical experiment, TEMPO-nanocellulose fiber slurry were dispersed in deionized water at the content of 0.1 wt%, and the suspension was stirred at 1000 rpm for 2 h. Two hundred gram of the above suspension was vacuum filtered for 4-6 h with a glass filter holder (XX1009020, EMD Millipore Corporation. ) using a hydrophilic PVDF filter membrane (VVLP09050, EMD Millipore Corporation, pore size: 0.1 μm) . After filtration, a wet transparent gel was formed on top of the filter membrane. Once peeled off from filter membrane, the gel “cake” (7 cm in diameter) was first carefully stacked between two plastic ring and stored in the 40 ℃ oven for 4 h for drying. Next, the dried NFC paper was placed between two Teflon film and hot pressed under pressure (2.6 MPa) at 75 ℃ for 5 min.

NanoPAD Fabrication: Inlets, outlets and channels on both NFC paper and EVA film were designed using Solidworks software and cut by a laser machine. After cutting, five layers were aligned, pressed between two glass slides by using 4 clips and then stored in an oven at 75 ℃ for 20 min to melt the EVA film. Next, the device was cooled down to room temperature for further use.

NFC Paper Characterization: The morphology of NFC was acquired using a Philips Technai G2 20 TEM (FEI, US) equipped with a Gatan imaging filter operating at 120 kV. The NFC sample for TEM was prepared as reported previously. Specifically, 5 uL 0.1%w/w NFC suspension was first dropped on positively charged TEM grids which was dried using filter paper after 2 min. Next, these grids were stained by depositing 2 uL of a 0.1%w/v solution of poly-L-lysine and 2 uL 0.4 %w/v solution of uranyl acetate successively which were removed with filter paper after 2 min.

The transmittance of NFC paper and absorption spectra of gold nanostars were obtained with a UV-vis spectrometer (SpectraMax M5, Molecular Devices, Sunnyvale, CA) . An ultrafast Atomic Force Microsope (AFM) (JPK Nanowizard@3, Berlin, Germany) was applied to characterize the surface of the NFC paper. 2 uL Au nanostars sample was deposited on TEM grids and dried in air. TEM was used to characterise its size and shape.

Au Nanostars Synthesis: Highly branched Au NSs were synthesized using a previously reported one step method. Briefly, 100mM solution of HEPES was prepared in DI water and pH was adjusted to 7.4 by using 1M NaOH. Next, 2 ml of HEPES solution were mixed with 3 ml of DI water and 50 μl of 20mM solution of gold (III) chloride hydrate solution in a glass vial. The vial was kept at room temperature for 60 minutes without shaking. The colour of the mixture changed from light yellow to colorless to light pink and finally dark blue over a period of 20 minutes. The reaction was allowed to complete for one hour. Then the sample was centrifuged and washed for twice, with a step of concentration to 20x followed.

SERS Measurement: All of the Raman spectra were measured using a confocal Raman spectroscopy (inVia ^TM, confocal, Renishaw) equipped with a 633 nm laser source and a CCD detector. Once samples were introduced into inlets of hollow channels, the Au nanostars area was focused using 50×objective lens. The signals were collected with 10 mW laser power, for 10 s exposure time. Subsequently, the Raman spectrum was acquired in the wavenumber range of 400 to 1800 cm ^-1 with a spectral resolution of 1 cm ^-1. A baseline correction routine was performed on the spectral data to obtain the final spectrum with the background subtracted. All the spectral data were analyzed using Origin Lab software.

Experimental Results

Fig. 1 shows an illustration of NFC paper and its characterization. The morphology of NFC was first investigated as shown in Fig. 1a. The diameter of NFC is 10±1 nm and their lengths are 500 nm or longer. Our NFC was processed using TEMPO-mediated oxidation; therefore its diameter size is uniformly distributed and can reach down to 10 nm. Fig. 1b shows a photograph of the transparent NFC paper after hot pressing at 75 ℃. The size of this paper is 70 mm in diameter. Higher hot-pressing temperature like over 100 ℃ can deteriorate the transmittance of NFC paper due to TEMPO-mediated oxidation. However, phenomenon of brown discoloration under high temperature can be reduced using the chemically modified protocol. If future projects required. Fig. 1c presents the transmittance of NFC paper in the wavelength range of 350～800 nm. It can be found that its transmittance is over 95%and close to 100%that is the transparency of a PET film. This high transparency can be explained from its nanoscale diameter of the cellulose, its smooth surface and the nanoscale porosity of NFC paper (Fig. 1d) so that light can go through this paper film easily with little light scattering effect. This property can be a huge advantage on the application of a transparent hollow-channel nanoPAD integrated with optical detection technologies. Fig. 1d shows the surface roughness characterized by AFM over a 1 μm × 1 μm of NFC paper area. The maximum surface roughness depth was estimated to be 6 nm. This low surface roughness is comparable to that of widely used plastic substrates (e.g. PET film) and PDMS substrates, which allow fluid flow much more freely in hollow channels. From Fig. 1d, it can be also estimated that the pore size distribution of NFC paper is around 20 nm. This nanoscale porosity can be a very important aspect for hollow-channel paper devices. This character can enhance the liquid holding capability of NFC paper to reduce vertical solution permeability.

Fig. 2a illustrates an exploded schematic of a hollow-channel nanoPAD. This device is assembled using five layers of film: the top, middle and bottom layer are NFC paper as substrates; the second and forth layer are EVA films as its bonding material. Channels in the middle are for fluid transportation using laser cut. Fig. 2b presents the photography of a transparent hollow-channel nanoPAD with channel widths of 1, 2 and 3 mm. It can be found that the transparency of bonding part was not reduced by EVA films. This phenomenon can be explained that during thermal bonding, the melt EVA can fill into the nanoscale pores of NFC paper and light can pass through the bonding layer even much more easily. No lateral leakage was observed in previous experiments. Therefore, EVA film can be a good candidate of bonding material in our application. The fluid permeability of hollow channels was also tested by passing red dye through an enclosed NFC paper channels. No vertical leak can be observed in five tests using devices in fig. 1b. These results can be used to confirm the feasibility of NFC paper as the substrate of a microfluidics device.

Next, the wicking capability of hollow-channel nanoPAD was characterized using 150-um-high hollow channels with widths of 1 mm, 2 mm and 3 mm. To eliminate fluid pressure effect on flow speed, channels were vertically placed above red dye solution reservoir, where driven force only comes from the difference of capillary pressure and atmosphere pressure. From the measurement results shown in Fig. 2c, it can be found that, flow speed in a 2-mm-wide channel decreases with the rise of fluid front, as expected. The fluid front stopped at the height of around 20 mm because flow resistance increases a lot as the wicking of fluid front in the channel. Then the difference of wicking ability among channels with different width was compared here. Fig. 1d shows the measurement results of wicking speeds among channels with widths of 1, 2 and 3 mm when the fluid height is 10 mm. Much faster wicking speeding can be found in a wider channel because of its greater surface tension. These characterization data can be applied to design hollow channels with desired flow speeds, e.g. fluidic timing.

For biosensing demonstrations, this 2-mm-width transparent hollow-channel nanoPAD design was firstly used as a SERS platform. Slightly different from device fabrication methods introduced previous, before thermal bonding, surface coating of gold nanostars as SERS substrates was done in the middle of bottom NFC layer. The morphology of Au NSs was characterized by TEM as shown in Fig. 5a. It can be found that the size distribution of Au NSs (around 50 nm in diameter) was relatively uniform and sharp edges on the Au NSs can be seen from the inset. The UV-vis absorbance curve of AuNSs solution with a peak at 595 nm was shown in Fig. 5b. The inset includes a photo of Au NSs suspension in dark blue colour. RhB molecules were used as Raman reporters for the achievement of quantitative detection. In a 2-mm-width channel, after 4 μL of RhB solution was introduced from its inlet to the SERS measurement area, the Raman signals were obtained to detect RhB concentration. The possibility of proposed SERS probe for the quantification of RhB in deionized water was tested.

Fig. 3a showed the experimental results of Raman spectra of RhB at various concentrations from100 nM to 1 mM. Except at 100 nM, prominent Raman peaks were found in RhB solution. The band intensity at 1650 cm ^-1 illustrated aromatic C–C stretching mode that was selected as the representative peak to detect RhB concentration because of the most significant change resulting from the increase in RhB concentrations. Aromatic C–C peak intensity at 1650 cm ^-1 increased depending on the increasing of RhB concentration in the range of 10 ^-6 M to 10 ^-3 M in water sample. From Fig. 3b, it is found that the log of SERS intensities at 1650 cm ^-1 and the log of concentration of RhB have a linearity (R ²=0.9) in the range of 10 ^-6 M to 10 ^-3 M. Based on these results, our transparent hollow-channel nanoPAD will be a promising platform for SERS or other optical detection platforms in the future, e.g. biological detection and environmental contaminants detection.

Then this transparent hollow-channel nanoPAD was used for the achievement of quantitative detection of glucose as colorimetric assays. 3 uL of PBS solution spiked with reagents, including glucose oxidase (120 U mL ^-1) and horseradish peroxidase (30 U mL ^-1) as oxidation enzyme, trehalose (0.3 M) as stabilizer, 4-aminoantipyrine (0.2 M) and 3, 5-dichloro-2-hydroxy-benzenesulfonic acid (0.4 M) as oxidation indicator, was used to prepare the nanoPAD with detecting reagents (the dimension of hollow channel is 2 × 5 × 0.15 mm ³) . After the reagents were dried, 3 uL of artificial urine spiked with glucose at the different concentrations (4 mM-20 mM) was introduced from the channel inlets of nanoPAD. Colorimetric reactions for detecting glucose was based on the oxidation of this analyte by glucose oxidation enzyme with hydrogen peroxide produced. Then the color of oxidation indicator was changed due to the oxidation reaction with the generation of hydrogen peroxide. A desktop scanner (LiDE 210, Cannon, Japan) was used to measure the colorimetric signals after 10-min reactions. Photos were converted to gray scale. Color intensities and gradients were analyzed using

As shown in Fig. 4a, the color of a whole hollow channel is quite uniform and gradually change from light to dark red as the increase of glucose concentration. From Fig. 4b, a good linearity between the glucose concentration and color grayscale intensity was obtained in the range of 4 mM-20 mM (R ²=0.98915) . Based on these results, our transparent hollow-channel nanoPAD will be a promising platform for colorimetric bioassays in the future.

In the invention, NFC paper was the first time applied as the substrate of paper-based hollow-channel microfluidics. By simply Using EVA as the material of thermal bonding, a novel highly transparent hollow transparent paper device was easily created. Importantly, the presented technique was shown to enable pump-free flow transfer. Major fabrication parameters for controlling the wicking speed were characterized, providing guidelines for designing this type of paper-based devices. Using this simple design, a colorimetric detection of glucose was demonstrated. Also, its compatibility with the optical detection was tested by using SERS to monitor RhB. This technique, we believe, can significantly broaden the application of paper-based microfluidics.

The above description is only preferred embodiments of the present invention and not intended to limit the present invention, it should be noted that those of ordinary skill in the art can further make various modifications and variations without departing from the technical principles of the present invention, and these modifications and variations also should be considered to be within the scope of protection of the present invention.

Claims

A Nanofibrillated-cellulose-paper-based microfluidic device comprising a transparent hollow channel fluidly connecting a fluid inlet to a fluid outlet, wherein

the transparent hollow channel comprise a fluid flow path defined by a floor, two or more side walls, and a ceiling,

the floor comprises a transparent nanofibrillated cellulose paper, and

the ceiling comprises a transparent NFC paper.
The device according to claim 1, wherein the floor of the hollow channel comprises transparent hydrophilic NFC paper.
The device according to claim 1, wherein the ceiling of the hollow channel comprises transparent hydrophilic NFC paper.
The device according to claim 1, wherein the side walls of the hollow channel comprise a hydrophobic material.
The device according to claim 1, wherein the side walls of the hollow channel are selected from the group consisting of a hydrophobic material, a hydrophilic material, and any combinations thereof.
The device according to claim 4 or 5, wherein the hydrophobic material comprises a paper covalently modified to comprise a hydrophobic agent, paper impregnated with a hydrophobic agent, a paper coated with a hydrophobic agent, or any combinations thereof.
The device according to claim 5, wherein the hydrophilic material is selected from the group consisting of NFC paper, microfibrillated cellulose (MFC) paper, bacterial nanocellulose paper, and any combinations thereof.
The device according to any of claims 1-5, wherein the hollow channel transports a fluid without an external pressure applied to the inlet or outlet of the device.
The device according to any of claims 1-5, wherein the device further comprises an assay reagent in contact with the hollow channel.
The device according to any of claims 1-5, wherein the device further comprises a surface enhanced Raman scattering (SERS) substrate material in contact with the hollow channel.
The device according to claim 10, wherein the SERS substrate material is selected from the group consisting of gold nanostructures, silver nanostructures, nanostructures of any other materials with surface Raman enhancement effect, and any combinations thereof.
The device according to any of claim 1-5, wherein the device further comprises a detection device configured to measure an optical signal inside the hollow channel.
The device according to claim 12, wherein the detection device comprises a camera, a cell phone, a fluorescence meter, a spectrometer, or any combinations thereof.
A method of fabricating a Nanofibrillated-cellulose-paper-based microfluidic device comprising steps of:

providing a first paper sheet, a second paper sheet, a third paper sheet, and a bonding material,

cutting one or more openings on the first paper sheet or the third paper sheet to form a fluid inlet or outlet of the device,

cutting one or more openings on the second paper sheet to form the microfluidic channel patterns,

bonding the first paper sheet and the second paper sheet together using the bonding material,

bonding the third paper sheet onto the second paper sheet side of the bonded bilayer of the first and second paper sheets using the bonding material.
The method of fabricating a Nanofibrillated-cellulose-paper-based microfluidic device according to claim 14, wherein the first paper sheet and the third paper sheet respectively are selected from the group consisting of NFC paper, MFC paper, bacterial nanocellulose paper, and any combinations thereof.
The method of fabricating a Nanofibrillated-cellulose-paper-based microfluidic device according to claim 14, wherein the bonding material is selected from the group consisting of ethylene vinyl acetate, glue, double-sided adhesive tape, and any combinations thereof.
The method of fabricating a Nanofibrillated-cellulose-paper-based microfluidic device according to claim 14, wherein the cutting of the paper sheets is selected from laser cutting, blade cutting, or a combination thereof.
The method of fabricating a Nanofibrillated-cellulose-paper-based microfluidic device according to claim 14, wherein the bonding of paper sheets is selected from mechanical compressing, thermal compressing, and a combination thereof.
A method of fabricating a Nanofibrillated-cellulose-paper-based microfluidic device comprising steps of:

providing a first paper sheet, a second paper sheet, a third paper sheet, and a bonding material,

cutting one or more openings on the first paper sheet or the third paper sheet to form the fluid inlet or outlet of the device,

cutting one or more openings on the second paper sheet to form the microfluidic channel patterns,

bonding the first paper sheet and the second paper sheet together using the bonding material,

coating the microfluidic channel area of the first paper sheet with a SERS substrate material,

bonding the third paper sheet onto the second paper sheet side of the bonded bilayer of the first and second paper sheets using the bonding material.
The method of fabricating a Nanofibrillated-cellulose-paper-based microfluidic device according to claim 19, wherein first paper sheet and the third paper sheet are respectively selected from the group consisting of NFC paper, MFC paper, bacterial nanocellulose paper, and any combinations thereof.
The method of fabricating a Nanofibrillated-cellulose-paper-based microfluidic device according to claim 19, wherein the bonding material is selected from the group consisting of ethylene vinyl acetate, glue, double-sided adhesive tape, and any combinations thereof.
The method of fabricating a Nanofibrillated-cellulose-paper-based microfluidic device according to claim 19, wherein the bonding material can be a glue, a transparent double tape, or a combination thereof.
The method of fabricating a Nanofibrillated-cellulose-paper-based microfluidic device according to claim 19, wherein the SERS substrate material is selected from the group consisting of gold nanostructures, silver nanostructures, nanostructures of any other materials with surface Raman enhancement effect, and any combinations thereof.
The method of fabricating a Nanofibrillated-cellulose-paper-based microfluidic device according to claim 19, wherein the cutting of the paper sheets is laser cutting, blade cutting, or a combination thereof.
The method of fabricating a Nanofibrillated-cellulose-paper-based microfluidic device according to claim 19, wherein the bonding of paper sheets is mechanical compressing, thermal compressing, and a combination thereof.
The method of fabricating a Nanofibrillated-cellulose-paper-based microfluidic device according to claim 19, wherein the coating of the SERS substrate material is selected from the group consisting of casting and then drying of a solution of pre-synthesized SERS substrate material, in-situ synthesis of SERS substrate material, or a combination thereof.