ANALYTICAL SCIENCES AUGUST 2021, VOL. 37

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2021 © The Japan Society for Analytical Chemistry

Oxide Nanowire Microfluidic Devices for Capturing Single-stranded
DNAs
Marina MUSA,*1† Takao YASUI,*1,*2,*3† Zetao ZHU,*1 Kazuki NAGASHIMA,*2,*4 Miki ONO,*1 Quanli LIU,*1
Hiromi TAKAHASHI,*1 Taisuke SHIMADA,*1 Akihide ARIMA,*1 Takeshi YANAGIDA,*4,*5 andYoshinobu BABA*1,*3,*6†*1 Department of Biomolecular Engineering, Graduate School of Engineering, Nagoya University, Furo-cho,
Chikusa, Nagoya 464–8603, Japan*2 Japan Science and Technology Agency (JST), Precursory Research for Embryonic Science and Technology(PRESTO), 4-1-8 Honcho, Kawaguchi, Saitama 332–0012, Japan*3 Institute of Nano-Life-Systems, Institutes of Innovation for Future Society, Nagoya University, Furo-cho,
Chikusa, Nagoya 464–8603, Japan*4 Department of Applied Chemistry, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo,
Bunkyo, Tokyo 113–8656, Japan*5 Institute of Materials Chemistry and Engineering, Kyushu University, 6-1 Kasuga-Koen, Kasuga,
Fukuoka 816–8580, Japan*6 Institute of Quantum Life Science, National Institutes for Quantum and Radiological Science andTechnology, 4-9-1 Anagawa, Inage, Chiba 263–8555, Japan

Since DNA analysis is the fundamental process for most applications in biomedical fields, capturing DNAs with highefficiency is important. Here, we used several oxide nanowire microfluidic devices to capture CpG-rich single-stranded
DNAs (ssDNAs) in different pH solutions. All the oxide nanowires exhibited the highest capture efficiency around pH 7with good capture efficiency shown by each metal oxide; ZnO/ZnO core/shell NWs (71.6%), ZnO/Al2O3 core/shell NWs(86.3%) and ZnO/SiO2 core/shell NWs (86.7%). ZnO/Al2O3 core/shell NWs showed the best performance for capturing
ssDNAs under varying pH, which suggests its suitability for application in diverse biological fluids. The capturing
efficiencies were attributed to the interactions from phosphate backbones and nucleobases of ssDNAs to each nanowire
surface. This finding provides a useful platform for highly efficient capture of the target ssDNAs, and these results canbe extended for future studies of cancer-related genes in complex biological fluids.
Keywords Oxide nanowire, microfluidic device, single-stranded DNA, DNA capture, quantitative polymerase chain
reaction (qPCR)(Received November 27, 2020; Accepted January 15, 2021; Advance Publication Released Online by J-STAGE January 22, 2021)

Introduction
Since DNAs play important roles in living organisms as thecarrier of genetic information1 and DNA analysis is thefundamental process for most applications in biomedical fields,
capturing DNAs on various materials has been extensively
studied for biomedical applications including nucleic acidextraction,2,3 biosensing4–8 and gene delivery.9–11 The adsorptionof DNAs on solid surfaces has been investigated through various
interactions, which include electrostatic interactions,12,13hydrogen bonding and hydrophobic interactions,14,15 and π-π
coupling.4,16 Although most of the previous research highlighted
the adsorption of DNA through electrostatic interactions
between the positively charged surface and negatively charged
To whom correspondence should be addressed.
E-mail: marinamusa2210@yahoo.com (M. M.); yasui@chembio.
nagoya-u.ac.jp (T. Y.); babaymtt@chembio.nagoya-u.ac.jp (Y. B.)†

Anal. Sci., 2021, 37, 1139–1145
DOI:10.2116/analsci.20P421

phosphate backbone,6,12,13 in the case of single-stranded DNAs,
we need to consider interactions with the nucleobases, which
are readily exposed for interactions, and their charges that might
influence the adsorption.5 Besides, the interactions between
negatively charged oxide-based materials and negatively charged
phosphate backbones have been reported based on the hard-soft
Thus, finding compatible
acid-base (HSAB) principle.4
materials that can promote good interactions for capturing
DNAs has received considerable interest.
The task of DNA analysis includes the formidable challengeof capturing a low copy number of DNAs from complex
biological samples. Moreover, the availability of biologicalsamples in diverse pH; gastric juice (pH 1.32 – 3.57),17 bloodplasma (pH 7.2),18 liver bile (pH 7.8) and pancreatic juice (8.0 –8.3)19 has made the analysis more difficult. To overcome thesechallenges, a number of materials to capture DNAs have beenreported, including gold nanoparticles,20–23 metal oxides,2,12,13,24
graphene oxide (GO)4,16 and molybdenum disulfide (MoS2).8,25
Among the materials, applications of metal oxides have

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ANALYTICAL SCIENCES AUGUST 2021, VOL. 37

Fig. 1 Schematic illustrations for the fabrication of nanowires in microfluidic devices. (a) Precleaned fused silica substrate. (b) OAP spin coating. (c) OFPR-8600 spin coating. (d) Nanowire area
pattern formed by photolithography, followed by pattern development using NMD-3. (e) Formation of
ZnO seed layer by RF sputtering. (f ) Hydrothermal growth of ZnO nanowires. (g) Removal of OFPR8600 photoresist followed by ALD of ZnO, Al2O3, and SiO2. (h) Attachment of PDMS substrate byheating at 180°
C for 2 min. (i) Insertion of PEEK tubes into the inlet and outlet holes.

increased due to their good optical, electronic and catalytic
properties, and biocompatibility.22,26 Metal oxide nanowires
offer the advantages of a rigid framework28 and other diverse
properties, which include large surface-to-volume ratio and ease
Due to these advantages,of surface modification.29,30
applications of metal oxide nanowires to biomolecular analysis
have been emerging.29–32
In this research, we studied the performance of hydrothermallygrown zinc oxide nanowires (ZnO NWs) before and after
surface modification with ZnO (ZnO/ZnO core/shell NWs),
aluminum oxide (ZnO/Al2O3 core/shell NWs) and silicon
dioxide (ZnO/SiO2 core/shell NWs) using the atomic layer
deposition (ALD) method for capturing CpG rich singlestranded DNAs (ssDNAs). ssDNAs with CpG sites, which arenaturally found in microbial DNA, are always associated withthe biomarker of diseases due to epigenetic modifications,particularly abnormal methylation on the CpG sites that alter
gene expression.33,34 Hence, their analysis has become important.
The sequence of the ssDNAs used in this research was designedwith consecutive cytosine and guanine (C+G) portion greaterthan 50% of the total DNA length as representative of CpG-rich
DNA in cancer-related genes.35,36 Considering the different
properties of the chosen metal oxides, which include theirsurface potential and class in HSAB, we investigated theirperformance to capture the target ssDNAs under varying pH, toscreen their potential for applications in diverse biologicalfluids.

Methodology
Fabrication of ZnO nanowires
Steps in the fabrication of the ZnO nanowires on a patternedarea are shown schematically in Figs. 1a to 1f. A pre-cleaned
fused silica substrate, 20 × 20 × 0.5 mm in size (Crystal BaseCo., Ltd.) (Fig. 1a), was first spin-coated with 1,1,1,3,3,3-hexa
methyldisilazane (OAP, Tokyo Ohka Kogyo Co., Ltd.) and thenwith OFPR-8600 (Tokyo Ohka Kogyo Co., Ltd.) (Fig. 1b and1c, respectively). Next (Fig. 1d), a nanowire-fabricated areawith length and width of 10 and 5 mm, respectively, was formedby photolithography. The substrate was next immersed in
NMD-3 solution (Tokyo Ohka Kogyo Co., Ltd.) to develop thearea that was later used for growing nanowires. A seed layer ofZnO (thickness, 130 nm) was sputtered on the substrate for10 min using an RF-sputtering machine (SC-701Mk Advance,
Sanyu Electron Co., Ltd.) (Fig. 1e). A hydrothermal method
was applied to grow the nanowires by immersing the substrate
into a mixture of 40 mM hexamethylenetetramine (HMTA,
Wako Pure Chemical Industries, Ltd.) and 40 mM zinc nitratehexahydrate (Thermo Fischer Scientific Inc.), followed byheating at 95°
C for 3 h (Fig. 1f ).
ALD of ZnO, Al2O3 and SiO2 layers
After fabrication of the ZnO nanowires, the OFPR-8600
photoresist was removed (Fig. 1g) and an atomic layer
deposition (ALD) system (Savannah G2, Ultratech Inc.) wasused to deposit a thin layer of metal oxides with an approximate
thickness around 5 – 6 nm. The ALD conditions differeddepending on the type of metal oxides: i) ZnO (precursor,
diethylzinc (DEZ) and water; temperature, 100°
C, 55 cycles); ii)
Al2O3 (precursor, trimethylaluminum (TMA) and water;
temperature, 150°
C, 55 cycles); and iii) SiO2 (precursor,
tris(dimethylamino)silane (TDMAS) and ozone; temperature,
150°
C, 55 cycles).
Fabrication of PDMS microchannel
A 3-inch N-type <100> silicon wafer (Advantech Co., ltd.)
was spin-coated with 3 mL SU-8 3005 (Nippon Kayaku Co.,
Ltd.), followed by pre-baking at 95°
C for 3 min. The pattern for
microchannel was formed by photolithography process with UVenergy of 200 mJ/cm2. The silicon wafer was then baked at 65
and 95°
C for 1 and 2 min, respectively. The microchannel
pattern was developed using SU-8 developer (Nippon Kayaku
Co., Ltd.), rinsed with isopropyl alcohol (IPA) (Kanto ChemicalCo., Inc) and subjected to silanization treatment withtrichloro(1H,1H,2H,2H-perfluorooctyl)silane (Merck KgaA) for
2 h. The mold was later used to make a microchannel on apolydimethylsiloxane (PDMS) substrate by mixing Silpot184

ANALYTICAL SCIENCES AUGUST 2021, VOL. 37(Dow Corning Toray Co., Ltd.) and curing agent Catalyst
Silpot184 (Dow Corning Toray Co., Ltd.) at a ratio of 10:1. The
resulting PDMS microchannel with size of 10 mm length, 5 mm
width and 10 μm height was then punctured using a 0.5 mm
hole puncher (Harris Uni-Core) to make the inlet and outlet
holes.
Fabrication of oxide nanowire microfluidic devices
The final fabrication step of the devices with the nanowires in
the microchannel is shown schematically in Figs. 1h and 1i.
The surface of the PDMS substrate and the fused silica substratewith grown nanowires were treated using a plasma etchingapparatus (Meiwafosis Co. Ltd.). The two substrates werebonded together by heating at 180°
C for 2 min (Fig. 1h).
Polyetheretherketone (PEEK) tubes, 0.26 mm inner diameter ×
0.5 mm outer diameter (Institute of Microchemical Technology
Co. Ltd.), were then inserted into the inlet hole and the outlet
hole (Fig. 1i).
FESEM and STEM-EDS characterizations of nanowires
Surface morphologies of ZnO NWs and ZnO/ZnO core/shell
NWs were observed using a field emission scanning electron
microscope (FESEM) (SUPRA 40VP, Carl Zeiss AG).
Elemental mappings of the Al2O3- and SiO2-coated nanowires
were obtained using a scanning transmission electron microscope
equipped with an energy dispersive X-ray spectrometer (STEMEDS) (JSM-7610F, JEOL) operated at an acceleration voltage of
30 kV. The images were obtained with 512 × 384 pixels at scanrate of 0.1 ms. The images were integrated for 100 cycles andthe peaks of Zn Kα (8.630 keV), O Kα (0.525 keV), Al Kα(1.486 keV) and Si Kα (1.739 keV) were used to construct theimages.

1141
Zeta potential measurement
The zeta potential of 50 ng/L DNA in Millipore water solution
was measured at 25°
C using a dynamic-light scattering
spectrophotometer (ZETASIZER Nano-ZS Malvern Panalytical).
For the metal oxide nanowires, ZnO/ZnO core/shell NWs, ZnO/
Al2O3 core/shell NWs and ZnO/SiO2 core/shell NWs were
fabricated on a 2.6 cm wide × 3.7 cm long × 0.1 cm glass
substrate followed by the zeta potential measurement (ELSZ2000, Otsuka Electronics) in Millipore water at 25°
C.
Capture experiment for ssDNAs using nanowire microfluidic
devices
The DNAs, primers and probes used in the capture experimentwere obtained from Invitrogen, Themo Fisher Scientific, Inc.
and their sequences are shown in Table 1. A DNA solution of
50 ng/L was prepared by dissolving the stock DNA in Millipore
water.
Hydrochloric acid (HCl, FUJIFILM Wako Pure
Chemicals Corp., Ltd.) and sodium hydroxide (NaOH, Wako
Pure Chemical Industries, Ltd.) solutions were used to vary the
pH of the DNA sample solution to pH 3, 7 and 10 and the pH
was measured using a pH meter (Horiba Scientific). The capture

Table 1

Sequence of the oligonucleotides used

Oligonucleotide

Sequence (5′ – 3′)

Probe
Forward primer
Reverse primer
61 Bases

FAM-ATCGCGCTCTCGCGCTGACGG
ACGCGTACTGCGGTCG
GCGTACGCGCGACG
ATACGCGTACTGCGGTCGCGATCGCGCTCTCGCGCTGACGGTGCGTCGCGCGTACGCGATT

Fig. 2 Characterizations of metal oxide nanowires. (a) FESEM images of ZnO nanowires and ZnO/ZnO nanowires, top and cross-sectional views. (b) Size distribution of diameter and length of ZnO/ZnO core/shell nanowires. The number of measurements for diameter and length was 50. (b) STEMEDS elemental mapping of ZnO/Al2O3 and ZnO/SiO2 nanowires. For ZnO/Al2O3 nanowires, Zn, O andAl are respectively highlighted as green, red and orange for single elemental mappings, and Zn and Al
are respectively highlighted as green and red for dual elemental mappings. For ZnO/SiO2 nanowires,
Zn, O and Si are respectively highlighted as green, red and orange for single elemental mappings, andZn and Si are respectively highlighted as green and red for dual elemental mappings.

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ANALYTICAL SCIENCES AUGUST 2021, VOL. 37

Fig. 3 Capture experiment for ssDNAs using different oxide nanowires in microfluidic devices. (a)Overview for capture in microfluidic devices. The device was connected to a syringe pump and acollection tube. (b) Capture efficiency of ssDNAs on different oxide nanowires: fused silica substrates(no nanowires); ZnO nanowires on the fused silica substrates, ZnO/ZnO nanowires on the fused silica
substrates; ZnO/Al2O3 nanowires on the fused silica substrates; and ZnO/SiO2 nanowires on the fusedsilica substrates. Error bars show the standard deviation for a series of measurements (N = 3).
Experimental conditions: 50 μL of 50 ng/L DNA solution; flow rate 5 μL/min; sample pH 7.

experiment was performed using a syringe pump system (KDS200, KD Scientific Inc.) at a flow rate of 5 μL/min. Next,
50 μL of Millipore water was introduced to remove any possible
contaminations. Then, 50 μL of 50 ng/L DNA solution was
introduced into the inlet of the microfluidic device and therecovered amount was collected in a 1 mL centrifuge tube.
Quantifications of DNA
Analysis of the concentrations of recovered DNAs was
performed using the PIKOREAL 96 quantitative polymerase
chain reaction (qPCR) system (Thermo Fisher Scientific Inc.).
A mixture containing 1 μL DNA solution, 3.5 μL Millipore
water, 5 μL TaqMan® Gene Expression Master Mix (Applied
Biosystems, Thermo Fisher Scientific Inc.), and 0.5 μL Custom
TaqMan® Gene Expression Assays (Applied Biosystems,
Thermo Fisher Scientific Inc.) was pipetted into a 96-wellreaction plate, sealed with an optical seal (Applied Biosystems,
Thermo Fisher Scientific) and qPCR was conducted. The qPCR
was carried out using the following cycling protocol: 2 min at
50°
C, 10 min at 95°
C, 50 cycles of 15 s at 95°
C, and 1 min at
60°
C. The capture efficiency of ssDNAs was calculated using
the equation below.
% Capture efficiency =Amount of input DNA – Amount output DNA
× 100%
Amount of input DNA

Results and Discussion
ssDNA capture experiment using different oxide nanowire
microfluidic devices
We used zinc oxide nanowires (ZnO NWs) as the core
nanowires and coated them with selected metal oxides: zincoxide (ZnO/ZnO core/shell NWs), aluminum oxide (ZnO/Al2O3
core/shell NWs) and silicon dioxide (ZnO/SiO2 core/shell NWs)
for the capture of target ssDNAs. Our previous research
reported on the optimal spacing between nanowires for capturing
the target ssDNAs as they traversed through the nanowires.37
Hence, the ALD method for the fabrication of the core/shell
nanowires was designed to give an approximate thickness of
5 – 6 nm to yield a similar size of nanowires for all metal oxides
in order to achieve the optimal spacing between nanowires. The
top and cross-sectional SEM views of the ZnO NWs and ZnO/ZnO core/shell NWs showed slight increments in the nanowire
size for ZnO/ZnO core/shell NWs (Fig. 2a). The size distributionof ZnO/ZnO core/shell NWs was representative of the core/shell
nanowires that gave a maximum peak in the range of 80 – 100 nm
and 1.4 – 1.5 μm, for the diameter and length, respectively(Fig. 2b). The STEM-EDS elemental mappings of ZnO/Al2O3
and ZnO/SiO2 nanowires indicated successful deposition of athin layer of Al2O3 and SiO2 on the ZnO nanowires using the
ALD method (Fig. 2c). ssDNAs were supplied into the oxide
nanowire microfluidic devices using the syringe pump systemand captured on the nanowires, while the uncaptured ssDNAs
were collected and quantified using qPCR (Fig. 3a). The
performance of different oxide materials for capturing ssDNAs

ANALYTICAL SCIENCES AUGUST 2021, VOL. 37

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Fig. 4 The effect of pH values on capture efficiency of different oxide nanowires. (a) Zeta potentialof ssDNAs and each nanowire type at pH = 7. (b) Zeta potential of ssDNAs at different pH. (c)Influence of pH on the capture of ssDNAs on ZnO/ZnO, ZnO/Al2O3 and ZnO/SiO2 nanowires. Error
bars show the standard deviation for a series of measurements (N = 3). Experimental conditions: 50 μL
of 50 ng/L DNA solution; flow rate 5 μL/min; sample pH 3, 7 and 10.

in neutral pH indicated an enhancement in capture efficiency bymetal oxide nanowires compared to the fused silica substrate
due to a larger surface-to-volume ratio possessed by the
nanowires (Fig. 3b). Surface modification of ZnO NWs withthin layer ZnO by ALD yielded ZnO/ZnO core/shell NWs that
improved the capture efficiency from 60.5 to 71.6%, possibly
due to the increase in nanowire size resulting in the optimal
spacing between nanowires sufficient for capturing the ssDNAs.
As such, core/shell NWs were used in subsequent studies.
Relationship between zeta potential and capture efficiency
To understand the effect of surface charge on capture efficiency
of ssDNAs, we measured the zeta potential of the metal oxide
nanowires and ssDNAs at neutral pH (Fig. 4a). ssDNAs showeda negative zeta potential value, –15.4 mV, due to thedeprotonation of hydroxyl from phosphates, and for the metaloxide nanowires, ZnO/ZnO core/shell NWs and ZnO/Al2O3
core/shell NWs showed positive zeta potential values, +15.4 mV
and +32.9 mV, respectively whereas ZnO/SiO2 core/shell NWs
exhibited negative values of –24.8 mV. Based on the assumptionthat the capture efficiency is related to only charged-based
interactions between the surface of nanowires and phosphatebackbone of ssDNAs, the highest capture efficiency should be
exhibited by ZnO/Al2O3 core/shell NWs (86.3%) or ZnO/ZnO
core/shell NWs (71.6%) followed by ZnO/SiO2 core/shell NWs(86.7%). However, our studies showed that all of the metaloxide nanowires exhibited good capturing performance for
ssDNAs near neutral pH (Fig. 3b), and ZnO/SiO2 core/shell
NWs exhibited the highest capture efficiency, which contradicts
previous reports that highlighted the contribution to DNA
capture as mainly being electrostatic interactions to negativelycharged phosphate backbone.6,13

Effect of pH on capture efficiency of different oxide nanowires
To investigate the capability of the metal oxide nanowires for
capturing ssDNAs in diverse biological fluids, we performed thecapture experiment under varying pH; pH 3, 7 and 10, which
covered the range of pH for most biological fluids. The zeta
potential of the ssDNAs under different pH conditions showed adecline in the values with increasing pH (Fig. 4b), and all of themetal oxides showed an increasing trend in capture efficiency
from pH 3 to 7, followed by a decreasing trend to pH 10(Fig. 4c). We supposed that lower capture efficiency exhibitedat pH 3 and 10 compared to pH 7 might be influenced by the
charge of nucleobases as reported in previous research.5,38 As
the nucleobases are stable in their neutral form in the range ofpH 5 to 8, their charges are tunable at lower and higher pH.39 At
pH 3, all of the metal oxides tend to be positively charged,
which caused repulsion between the metal oxides and positively
charged cytosine (pKa, 4.2) and adenine (pKa, 3.5).39,40 At more
extreme conditions, pH 10, the surface charge of ssDNAs tuned
to a highly negative charge as exhibited by the zeta potential
value (–27 mV) (Fig. 4b) due to the negatively charged
phosphate backbone and the deprotonation of guanine (pKa,
9.2 – 9.6) and thymine (pKa, 9.9)41 which inhibited theinteractions with the negatively charged metal oxides. Apartfrom the charge on the phosphate backbone, the charge ofindividual nucleobases should be taken into consideration as it
might have some influence on the capture efficiency.
The highest capture efficiency was reported at pH 7 for all
metal oxides, which suggested a more preferable interaction to
ssDNAs bearing neutral charged nucleobases with core/shell
NWs. More interestingly, ZnO/SiO2 core/shell NWs, which
possessed negatively charged surfaces showed higher capture
efficiency than positively charged ZnO/ZnO core/shell NWs.

1144
Other than the effect of surface charges, we supposed that therelation between the capture efficiency and HSAB principle
played an important role as reported in previous research basedon the interactions between several metal oxides and phosphates
according to this principle.4,42–44 In our case, both ZnO/Al2O3
core/shell NWs and ZnO/SiO2 core/shell NWs are classified as
hard acids, which have preferable affinity towards the phosphatesthat are classified as hard bases; on the other hand, ZnO/ZnO
core/shell NWs are classified as a borderline acid, which will
have a different affinity towards the phosphates.45–47 Higher
capture efficiency exhibited by ZnO/SiO2 core/shell NWs
compared to ZnO/ZnO core/shell NWs might be attributed tomore preferable interactions between hard acid and hard basecompared to those between borderline acid and hard base. ZnO/
Al2O3 core/shell NWs, which are classified as hard acid, canalso promote electrostatic attraction with ssDNAs, leading tohigh capturing performance of ssDNAs in a wide range pH
compared to the other metal oxides.

Conclusion
We fabricated different types of core/shell nanowires, ZnO/ZnO
core/shell NWs, ZnO/Al2O3 core/shell NWs and ZnO/SiO2 core/shell NWs in microfluidic devices, and we demonstrated theirperformance for capturing CpG-rich ssDNAs. The influence ofpH on the capture efficiency of ssDNAs was investigated from
low to high values of pH with the highest capture efficiency
achieved at pH 7 for all metal oxides. We concluded that for
capturing ssDNAs, apart from the role of the phosphatebackbone, the role of nucleobase should be taken into
consideration due to the unbound nucleobase side that makes it
readily exposed for interactions. Depending on the type ofmetal oxides, the capturing ability might vary due to the different
properties of each metal oxide. Our findings showed thecapability of the negatively charged surface of ZnO/SiO2 core/shell NWs to capture ssDNAs with high capture efficiency atneutral pH, despite having similar surface charge, thus
eliminating the effect of surface charge as the only factor for
capturing ssDNAs. Thus, other than the effect of surface charge,
we suggest that the HASB principle should be taken into
consideration when capturing ssDNAs onto oxide nanowire
surfaces. We proposed that for capturing ssDNAs, ZnO/Al2O3
core/shell NWs showed good potential to be applied in diverse
biological fluids due to high capture efficiencies exhibited undervarying pH compared to ZnO/ZnO core/shell NWs and ZnO/
SiO2 core/shell NWs. This finding provides prospects for more
expanded applications of the oxide nanowires in microfluidic
devices to the analysis of CpG rich ssDNAs in cancer-related
genes as well as the analysis of circulating microRNAs indiverse biological fluids.42

Acknowledgements
This research was supported by PRESTO (PMJPR19H9), Japan
Science and Technology Agency (JST), the JSPS Grant-in-Aid
for Young Scientists (A) 17H04803, the JSPS Grant-in-Aid for
Exploratory Research 20K21124, the JSPS Grant-in-Aid for
Scientific Research (S) 18H05243, the JSPS Grant-in-Aid for
Scientific Research (B) 18H02009, the JSPS Grant-in-Aid for
Scientific Research on Innovative Areas “Chemistry for
Multimolecular Crowding Biosystems”, and research grants
from each of the following: the Murata Science Foundation,
Advanced Technology Institute Research Grants 2019,

ANALYTICAL SCIENCES AUGUST 2021, VOL. 37
Foundation of Public Interest of Tatematsu, the Nitto Foundation,
the G-7 Scholarship Foundation, and the Cooperative Research
Program of the “Network Joint Research Center for Materials
and Devices”.

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