Research Update: Mesoporous sensor nanoarchitectonics

In this short review, we have selected three main subjects: (i) mesoporous materials, (ii) sensing applications, and (iii) the concept of nanoarchitectonics, as examples of recent hot topics in nanomaterials research. Mesoporous materials satisfy the conditions necessary not only for a wide range of applications but also for ease of production, by a variety of simple processes, which yield bulk quantities of materials without loss of their well-defined nanometric structural features. Sensing applications are of general importance because many events arise from interaction with external stimuli. In addition to these important features, nanoarchitectonics is a concept aimed at production of novel functionality of whole units according to concerted interactions within nanostructures. For the combined subject of mesoporous sensor nanoarchitectonics, we present recent examples of research in the corresponding fields categorized according to mechanism of detection including optical, electrical, and piezoelectric sensing.

In this short review, we have selected three main subjects: (i) mesoporous materials, (ii) sensing applications, and (iii) the concept of nanoarchitectonics, as examples of recent hot topics in nanomaterials research.Mesoporous materials satisfy the conditions necessary not only for a wide range of applications but also for ease of production, by a variety of simple processes, which yield bulk quantities of materials without loss of their well-defined nanometric structural features.Sensing applications are of general importance because many events arise from interaction with external stimuli.In addition to these important features, nanoarchitectonics is a concept aimed at production of novel functionality of whole units according to concerted interactions within nanostructures.For the combined subject of mesoporous sensor nanoarchitectonics, we present recent examples of research in the corresponding fields categorized according to mechanism of detection including optical, electrical, and piezoelectric sensing.© 2014 Author(s).All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.
[http://dx.doi.org/10.1063/1.4868177]Preparation and functionalization of nanostructured materials have been aggressively researched in the fields of applied chemistry and physics.The systems investigated usually possess three important features: (i) type of material used, (ii) required application, and (iii) concept of research.Most of the examples can be defined using a combination of these parameters, which effectively determine the focus of the research.In this short review, we have selected the following parameters: (i) materials with mesoporous structures, (ii) sensing (as an application field), and (iii) nanoarchitectonics as the research concept, in order to highlight recent hot topics in nanomaterial research involving these features.The motivation for the selection of these three parameters is briefly explained below.
Nanostructured materials, which can be applied for a wide range of uses, should be produced in a series of easy processes yielding large quantities of materials without loss of their well-defined nanometric structural features.Mesoporous materials [1][2][3][4][5] satisfy these conditions.As is well known, mesoporous materials possess regular pore arrays with diameters in the range from 2 to 50 nm with extremely large specific surface areas and specific pore volumes.Therefore, sensing properties based on size-discrimination can be anticipated for mesoporous materials. 6In addition, these materials can be produced using low cost material sources such as surfactants, polymers, silica, and carbon.At the same time, their structural dimensions are precisely defined by the template structures such as self-assembled micelles.Synthetic procedures mostly involve simple procedures of mixing, filtration, drying, and calcination (or solvent extraction).Mesoporous materials are some of the most attractive nanostructured substances having both fine structural precisions and practically available production processes.From the viewpoint of applications, sensing [7][8][9] is of general importance for various functionalities because sensing events arise from some external stimuli.Therefore, sensing can be regarded as detection of the initiating process of various functional events.For these reasons, we have selected "mesoporous materials" and "sensing" as material type and application parameter, respectively.
Regarding the final parameter, we have here selected the novel concept of nanoarchitectonics, [10][11][12][13][14][15][16][17][18][19] which was originally proposed by Aono. 20This concept is aimed at producing novel functionality of whole units according to the concerted interactions within its nanostructures.Methods in nanotechnology generally apply separate techniques for control of nanostructured materials and systems.6][27][28][29] Nanoarchitectonics can be regarded as a concept beyond nanotechnology and can be considered the next step for nanotechnology.
In this short review, we have combined the three main parameters of mesoporous materials (the material), sensing (the application), and nanoarchitectonics (the concept) as an overview of recent research in the corresponding fields.For an easier understanding, the examples introduced here are classified according to the sensing mechanism including optical sensing, electrical sensing, and piezoelectric sensing.
Because optical signals are simple to detect, optical sensing has been widely used.Optical sensing using mesoporous structures can be roughly classified into three categories (i) optical response based on specific interaction, (ii) optical probe release, and (iii) plasmon resonance and others, according to their sensing mechanisms.
Immobilization of photoactive groups on mesoporous materials is an advantageous strategy for optical sensing.Jun and co-workers reported a turn-on fluorescence sensor for CN − using cubic mesoporous graphitic carbon nitride with Cu 2+ . 30Cubic mesoporous graphitic carbon nitride was synthesized by a nanocasting method using ordered mesoporous silica KIT-6 as a hard template to which Cu 2+ was added as Cu(NO 3 ) 2 .Bound Cu 2+ captures photo-excited electrons leading to quenching of the photoluminescence of the cubic mesoporous graphitic carbon nitride.Displacement of Cu 2+ by CN − switches back on the photoluminescence, resulting in turn-on fluorescence sensing without interference from other anions and serum proteins.Therefore, this sensing system can be used under aqueous as well as physiological conditions.
Ha and co-workers synthesized sensing support materials referred to as SAPy (conjugate unit from salicylaldehyde and 4-aminomethylpyridine) modified mesoporous silica (see Figure 1). 31This material can be used for sensing of Fe 2+ (dark brown, λ max 325 nm at pH = 8) and Cu 2+ (green, λ max 365 nm at pH = 12) with a distinguishable colour change while the absorbance maximum of the metal free SAPy mesoporous silica was at 410 nm.The corresponding detection limit was approximately 50 ppb.Formation of metal complexes caused an internal charge transfer (ICT), resulting in the wavelength shift and colour change.This approach is capable of screening for Fe 2+ and Cu 2+ in competitive media by naked-eye observation.Li and co-workers demonstrated the importance of statistical data analyses in sensing. 32They immobilized ionic liquid receptors on a silica matrix and found that LUMO-HOMO energies, excitation and emission spectra, and fluorescent lifetimes were significantly influenced by coupling with different counterions.Statistical methods such as principal component analysis (PCA) and linear discrimination analysis (LDA) were used for further analyses.
Tang and co-workers immobilized the aggregation-induced emission luminogen, tetraphenylethene, onto amine-functionalized mesoporous silica. 33The materials used exhibited supersensitive fluorescence quenching to the nitroaromatic compound 2,4,6-trinitrophenol (picric acid) in aqueous solution because of photoinduced electron transfer and/or energy transfer.Picric acid molecules diffused into mesopore channels and were adsorbed to remaining amino groups  through acid-base interactions thus approaching tetraphenylethene groups.Contact of picric acid and tetraphenylethene facilitated electron transfer.In addition, overlap of the absorption spectrum of picric acid and the emission of fluorescent mesoporous silica at 380-487 nm induced energy transfer from the excited state of the fluorescent mesoporous silica to the ground state of picric acid.As a result, fluorescence quenching was facilitated.This system can be used repeatedly after washing with proper solvents since the tetraphenylethene is covalently immobilized.
Inagaki and co-workers prepared periodic mesoporous organosilica (PMO) in which fluorescent biphenyl (Bp) groups were densely immobilized and receptor 2,2 -bipyridine (Bpy) units were included (Figure 2). 34This periodic mesoporous organosilica structure provided an ideal arrangement of fluorophores and receptors because numerous fluorophores surround the receptor placed in the rigid nanochannels.Energy funneling into the Bpy receptor from a large number of Bp groups in the framework of periodic mesoporous organosilica results in enhanced emission of the Bpy receptor.This enhanced emission can be quenched or shifted in wavelength through interactions with ionic species.For example, Bpy emission was efficiently quenched by the addition of even a low concentration of Cu 2+ .In contrast, red shifts were observed after addition of Ag + , Hg 2+ , Zn 2+ , Cd 2+ , and Pd 2+ .Complex of Cu 2+ with a partially filled d 9 shell often is not emissive, while complexes of Ag + , Zn 2+ , Hg 2+ , and Cd 2+ with a closed-shell d 10 configuration are usually emissive.
Sun et al. synthesized anionic metal-organic frameworks (MOFs) with one-dimensional mesoporous channels that were assembled using 5,5 ,5 -(1,3,5-triazine-2,4,6-triyl)tris-(azanediyl)triisophthalate as a predesigned size-extended hexatopic ligand. 35These materials can selectively adsorb and separate cationic dyes.Separation occurs based on ionic selectivity rather than the size-exclusion effect in contrast to the previous examples of porous materials.Therefore, this system enables separation of large molecules with similar sizes but opposite charges.The presence of the imino triazine backbone and carboxyl groups of the hexatopic ligand also induced unusual solvatochromic phenomena in the presence of acetone and ethanol guests.
Lü and co-workers developed functional mesoporous silica materials that can sensitively detect trinitrotoluene through fluorescence resonance energy transfer (FRET). 36For this purpose, they introduced poly(p-phenylenevinylene) into mesoporous silica nanoparticles through an ion-exchange and in situ polymerization method.3-Aminopropyltrimethoxysilane was also immobilized as a binding site for trinitrotoluene.Trinitrotoluene and the immobilized amino group form Meisenheimer complexes between the electron-deficient aromatic rings and electron-rich amine ligands through a charge-transfer complexation interaction.The complex formed absorbs in the green region of visible light resulting in strong suppression of the fluorescence emission of poly(p-phenylenevinylene) by a FRET mechanism.
Ren and co-workers reported hierarchic mesoporous zeolite nanocomposites for sensitive detection and subsequent removal of Hg 2+ . 37Magnetic nanoparticles were immobilized in a mesoporous zeolite nanonetwork, and rhodamine-hydrazine was connected at the surface.Rhodamine-hydrazine is essentially non-fluorescent in its apo-state because of efficient photoinduced electron transfer quenching of the fluorophore by the lone pair of electrons on the nitrogen atom of the benzoyl moiety.Binding of Hg 2+ induced a drastic increase of the fluorescence intensity at 575 nm upon excitation at 540 nm owing to the delocalized xanthene moiety of the rhodamine group.Hg 2+ ion can be simultaneously removed by using the magnetic property of the nanocomposites.
Mesoporous materials can store significant amounts of optical probe species in their nanochannels.When optical probes are released upon recognition of target guest species, detection events can be transformed into an optical signal.Eritja and co-workers prepared an aptamer-capped mesoporous silica for the selective and sensitive detection of α-thrombin. 38They used MCM-41-type mesoporous silica as an inorganic scaffold into which a fluorescent probe molecule, rhodamine B, was loaded.The thrombin binding aptamer was immobilized at the silica surfaces, which had been modified with 3-aminopropyltriethoxysilane.Binding of α-thrombin to its aptamer removes the aptamer components opening the "gates" of the mesopore channels with concurrent release of rhodamine B. In vitro studies of this aptamer-modified mesoporous silica system revealed a limit of detection of 2 nM for α-thrombin.
Zhang and co-workers prepared DNA-functionalized mesoporous silica nanoparticles (MSN) for the rapid, sensitive, and selective detection of Hg 2+ in aqueous solution (Figure 3). 39The presence of Hg 2+ at ppb level destabilizes DNA hybridization, resulting in uncapping of the mesopore channels.High sensitivity is attributed to the selective binding of thymine-rich DNA with Hg 2+ .The latter event induces release of the dye cargo with detectable enhancement of fluorescence.Detection is very rapid (less than 20 min) with a limit of detection reaching 4 ppb.This superior sensing performance is also due to the large loading capacity of dyes in mesoporous silica nanoparticles.
Tang et al. developed protein-gated carbohydrate-functionalized magnetic mesoporous silica nanoparticles for sensitive detection of the small molecule mycotoxin, aflatoxin B1. 40 The monoclonal anti-aflatoxin B1 capture antibody was immobilized on concanavalin A-conjugated mesoporous silica particles loaded with rhodamine B by using the streptavidin-biotin interaction.Separately, gold nanoparticles were densely functionalized with invertase and aflatoxin B1 with bovine serum albumin.Specific competitive recognition for the immobilized anti-aflatoxin B1 antibody occurred between target aflatoxin B1 and the labeled aflatoxin B1 on the gold nanoparticle.After addition of sucrose, it is hydrolyzed to glucose by the immobilized invertase displacing the concanavalin A complex and uncapping the mesopore channels.As a result, loaded rhodamine B is released for detection.
Gupta and co-workers used catalytic signal amplification for the colorimetric detection of CN − in aqueous media (Figure 4). 41Their system utilized catalase in tandem with Fe-immobilized mesoporous silica nanoparticles (Fe-MSN) mimicking the enzyme horseradish peroxidase.The detection mechanism is based on several steps.The presence of CN − inhibits specifically the enzyme catalase, resulting in suppression of disproportionation of H 2 O 2 to water and oxygen.Activation of the residual H 2 O 2 by Fe-MSNs produces oxidized tetramethyl benzidine (TMB), which has a visually detectable green colour.They predicted that the limit of detection of the proposed system could be improved based on appropriate selection of reporter molecules with large extinction coefficients or which generate fluorescence upon oxidation.
Martínez-Máñez and co-workers prepared a unique system of lateral-flow assays based on antibody-gated dye delivery system using mesoporous silica. 42This test-strip-based lateral-flow assay system was used to detect triacetone triperoxide at the ppb level with an overall assay time of 2 to 10 min.Binding of triacetone triperoxide to an antibody cap induced release of dye at the  solvent front due to the flow conditions.The flow transports a certain amount of released dye away from the spot of mesoporous materials depending on the amount of triacetone triperoxide.
Charnay and co-workers prepared gold functionalized radial mesoporous silica nanoparticles. 43hese nanoparticles were then coated with phospholipid bilayers.The resulting hybrid structure plays the role of a biofunctional platform where gold metallic nanoparticles immobilized at the pore channels can exhibit plasmonic activity for biosensing.Sensing activity of this system upon adsorption of bovine serum albumin or for molecular recognition between avidin molecules and biotin receptors integrated in the supported lipid bilayer could be demonstrated.Mesoporous medium provides large surface areas and pore volumes with an accessibility to a variety of functional molecules or nanoparticles.Preparation of multifunctional plasmonic devices would be possible through surface bio-functionalization of the gold-functionalized mesoporous silica nanoparticles.
Langhammer and co-workers developed time-resolved nanoplasmonic sensing spectroscopy using mesoporous TiO 2 films in order to investigate dye molecule interaction in media such as dyesensitized solar cell device structures (Figure 5). 44Hidden-interface indirect nanoplasmonic sensing enables measurement of dye adsorption kinetics even of thick (10 μm in their case) mesoporous TiO 2 films.In this system, plasmonically active gold nanoparticles were placed at the hidden inner interface between a mesoporous TiO 2 layer and the support surface.Indirect nanoplasmonic signals could be measured simultaneously giving time-resolved and independent information about the interfacial and total amounts of dye adsorbed in the mesoporous TiO 2 film.The proposed measurement method also has significant potential for new insights into diffusion kinetics in porous catalyst systems, gas adsorption materials, and controlled release systems.Diffusion kinetics of several mesoporous structures has been compared in recent reports. 45,46 rsky et al. reported a method for real-time sensing of microorganisms such as bacteria and cells using photonic lamellar gratings of porous silicon. 47For two-dimensional arrays of a lamellar grating, the zero-order optical reflectivity exhibits an interference pattern similar to that obtained for reflective interferometric Fourier transform spectroscopy biosensors.The signals obtained can be Fourier-transformed into optical thickness resulting in sensing of rather large biological objects.
Sailor and co-workers developed a label-free optical biosensor using a porous silicon-carbon composite. 48The porous materials used were prepared by electrochemical anodization of crystalline Si, infiltration of poly(furfuryl) alcohol, and carbonization.Adsorption of rabbit and chicken IgG to the protein-A-modified porous silicon-carbon substrates was monitored by time-resolved measurement of reflective interferometric Fourier transform spectroscopy.Porous silicon-carbon materials exhibited good stabilities comparable with porous TiO 2 and superior to that of porous Al 2 O 3 .
Marsal and co-workers prepared gold-coated ordered nanoporous anodic alumina films for label-free biosensing based on reflective interferometric Fourier transform spectroscopy. 49For This article is copyrighted as indicated in the article.Reuse of AIP content is subject to the terms at: http://aplmaterials.aip.org/about/rights_and_permissionsDownloaded to IP: 14.139.212.242On: Mon, 12 Oct 2015 08:55:57 improvement of sensing signal outputs, a thin gold layer was deposited on the top of anodic aluminum porous structures.Increased refractive index contrast between the nanoporous alumina layer and the analytical aqueous solution led to significant contrast in the interferometric spectrum and a higher sensitivity of the structure.Sensing performance for detection of bovine serum albumin was significantly enhanced.
The superior features of regular mesoporous materials are also advantageous for other sensing methods.In the following paragraphs, non-optical sensing systems such as electrical/electrochemical and piezoelectric sensors using mesoporous materials are introduced.
Electrical responses: Electrical and electrochemical sensors have been widely used because the integration of such sensing systems as electric devices is rather easy so that introduction of mesoporous structures in electric and electrochemical devices is a promising approach.Zheng and co-workers prepared mesoporous SnO 2 materials for electrical gas sensing. 50Of the systems examined, sensor response increased with N 2 H 4 concentration from 5 to 500 ppm, and the sensor showed a very fast response and recovery.The response and recovery times for 100 ppm N 2 H 4 were only ca.70 s and 63 s at 260 • C, respectively.In contrast, a very weak response for NH 3 was found.
Zhou and co-workers fabricated mesoporous and hollow ZnO microspheres and investigated electrical gas sensing of ethanol and acetone at low concentrations. 51Response magnitudes increased with the test gas concentration from 5 ppm to 50 ppm.Within this concentration range, the sensor did not exhibit saturation behaviors.Wang and co-workers prepared mesoporous structures of p-type semiconductor Cr 2 O 3 for applications in gas sensors and lithium ion batteries. 52The mesoporous Cr 2 O 3 (in hexagonal and cubic phases) showed improved performance for vapor phase sensing of ethanol, acetone, and isopropanol as compared with the bulk Cr 2 O 3 material.High surface area, thin crystal walls, and narrow pore size distribution contribute to the improved sensor performance.
Wang and Yamauchi have been developing mesoporous metals and alloys that can be applied in various areas. 53Recently, they developed a novel strategy to fabricate mesoporous Pt-and Pt-based alloy films with large surface areas by electrochemical micelle assembly.In addition, programming of a square-wave potential resulted in formation of composition-controlled mesoporous Pt-Au alloy films.These Pt-Au mesoporous films are capable of electrochemical oxidation of glucose, and so can be used in highly sensitive glucose sensors.At fixed working potential (0.3 V), dynamic amperometric responses with successive increments of the glucose concentration from 0.00 to 1.05 mM was observed.Rapid increase in the current after each addition of glucose was confirmed in all cases.This mesoporous Pt-Au alloy-film system can be easily regenerated to their initial state only by rinsing with distilled water.The sensor electrodes maintained their activity for glucose sensing for at least ten cycles.
Dong and co-workers reported an electrochemical sensor for discrimination of D-vasopressin enantiomers using a split aptamer as a new chiral selector where a graphene-mesoporous silica-gold nanoparticle hybrid was used as the electrochemical sensing platform. 54Electrochemical probe ferrocene was covalently appended on poly(ethyleneimine) and assembled with poly(sodium 4styrenesulfonate) on the negatively charged indium tin oxide (ITO) electrode through LbL assembly.On this assembled film, two bilayers of graphene-mesoporous silica-gold nanoparticle hybrid were further assembled with counter polyelectrolyte, poly(ethyleneimine) with subsequent immobilization of D-vasopressin aptamer fragments.Mesoporous silica materials are capable of suppressing the nonspecific adsorption of the DNA.Hybrid structures with graphene and gold nanoparticles have good electronic conductivity, which is advantageous for the electronic transfer of probe molecules.
][57] Resonant frequency of a QCM device sensitively shifts in proportion to mass change on its electrode.The device sensitivity usually reaches nanogram-level or better.Mesoporous materials often provide appropriate media for QCM sensing.Ariga and co-workers assembled oxidized mesoporous carbon (CMK-3) with cationic polyelectrolyte on a QCM plate by the layer-by-layer (LbL) assembly method. 58Sensing performances for several substances were investigated in aqueous solution.A frequency shift upon adsorption of tannic acid to the CMK-3 LbL films was observed immediately after injection of tannic acid.Frequency shifts upon adsorption of tannic acid greatly exceed those FIG.6. Layer-by-layer films of mesoporous carbon capsule for gas sensing.
for catechin and caffeine.The superior adsorption capacity for tannic acid likely originates in π -π interactions and hydrophobic effects based on size fitting of tannic acid to the CMK-3 nanochannel.Adsorption quantities of tannic acid to the CMK Hi-LbL film at equilibrium exhibited a sigmoidal profile at low concentrations.The highly cooperative behavior observed might originate from confinement effects during adsorption, which may be similarly explained by enhanced guest-guest interactions.
As shown in Figure 6, carbon capsules synthesized using surfactant-coated zeolite crystals as templates were assembled in layer-by-layer manner with couterionic polyelectrolyte on a QCM plate that was used to detect specific molecules in gas phase. 59This sensing system showed better detection capabilities for aromatic hydrocarbons such as benzene and toluene than aliphatic hydrocarbons such as cyclohexane.π -π interactions probably play a crucial role in the adsorption of volatile guest in the carbon capsule film.Interestingly, impregnation with additional recognition components can alter gas sensing selectivity.The carbon capsule film impregnated with lauric acid showed the greatest affinities for non-aromatic amines.In contrast, impregnation of dodecylamine into the carbon capsule films resulted in a strong preference for acetic acid.
Yamauchi and co-workers modified QCM electrodes with size-controlled nanoporous carbon particles that were used for sensing of toluene molecules. 60The particles used were synthesized through carbonization of monodispersed zeolitic imidazolate framework-8 crystals.The QCM electrodes containing the small-sized nanoporous carbon clearly exhibited higher sensitivity upon uptake of toluene vapor.Sensor output reached stable values within a few minutes upon adsorption equilibrium.Interestingly, large-sized particles showed smaller adsorption despite their larger surface areas.Reduction of the particle size is probably advantageous for adsorption of toluene molecules onto the entire electrode.The same team used nanoporous carbon of large surface area for QCM sensing system. 61In this case, nanoporous carbon materials were prepared by direct carbonization of Al-based porous coordination polymers.Their superior structural characteristics of significantly high porosity resulted in superior sensing capabilities toward toxic aromatic substances.For example, sensing capability of this sensing system for benzene is approximately three times greater than for cyclohexane and hexane despite the three have similar molecular sizes and molecular weights.It is expected that graphitic carbon containing sp 2 -hybridized carbons should have higher affinities for aromatic hydrocarbons.
Yamauchi and co-workers synthesized hollow nanocubes of Prussian Blue (PB) analogue (Figure 7) that can be used for selective QCM sensing and removal of Cs ion. 62,63 he hollow particles were obtained by a synthetic route based on chemical etching with assistance of a protective reagent, polyvinylpyrrolidone (PVP).This process can be scaled up to mass production for environmental remediation.Prussian blue materials are known to be capable of significant adsorption of Cs ions.Further large adsorption uptake for Cs ions was due to the presence of a  huge hollow cavity that can promote the loading capacity of Cs ions.The same research group also prepared continuous cage-type mesoporous silica films with large spherical mesopores using polystyrene-block-polybutadiene-block-polystyrene triblock copolymers on a QCM sensor plate. 64n-line monitoring of water vapors was examined.In this synthesis, the framework thickness and pore-to-pore distance can be tuned without a significant size change of the original spherical mesopores, which are advantageous for water adsorption tests.This structural feature is also useful for both high loading capacity and slow release rate for anti-cancer drug delivery or for other efficient drug delivery systems.Not limited to mesoporous structures, PB materials are useful for the similar functions. 65,66 nu and co-workers reported photo-induced synthesis of COOH functionalized mesomacroporous carbon films. 67This material can be immobilized onto a QCM plate to provide excellent sensing capability for aromatic amines.Carboxyl groups were introduced on the surface of the porous carbon films using ozone treatment under photo-irradiation.In this approach, an amine-sensitive acid surface can be created without addition of toxic and/or environmentally hazardous oxidizing agents such as sulfuric acid, hydrogen peroxide or nitric acid.In turn, the same research group prepared QCM sensing systems for acetic acid using highly ordered nitrogen-containing mesoporous carbon. 68his nitrogen-containing mesoporous carbon was synthesized using a gelatin biomolecular precursor and SBA-15 mesoporous silica as a template via nanocasting method.These sensing systems are useful for the sensing of toxic acidic molecules including CO 2 and acetic acid.
Ishihara and co-workers fabricated a cage-in-fiber-type nanoporous carbon sensor selective for aniline (Figure 8). 69Electrospun nanofibrous films (poly(methyl methacrylate), PMMA) containing carbon nanocage materials were immobilized on QCM sensors.This hierarchic construction provides a greater surface area and a porous membrane structure advantageous for sensitive and rapid sensing.QCM sensing systems equipped with gas flow system allowed for detection of aniline at the ppm level with high selectivity over water, benzene, ammonia, and other chemical species.Aromatic amines such as aniline contained in cigarette smoke, broiled meats, some vegetables, and emissions This article is copyrighted as indicated in the article.Reuse of AIP content is subject to the terms at: http://aplmaterials.aip.org/about/rights_and_permissionsDownloaded to IP: 14.139.212.242On: Mon, 12 Oct 2015 08:55:57 from industries can be carcinogenic.Therefore, the real-time sensing system shown in this example could be highly useful for cancer risk management.
In this short review, we have collected together research examples of sensing applications using functional mesoporous materials.There exist a wide variety of modes of sensing because of the great freedom available in the structural design and synthesis, functionalization, and assembly of mesoporous materials.Several of the examples in this review strikingly illustrate the important features of nanoarchitectonics where structuring concepts such as mesopore formation and LbL assembly have been rationally combined.Since most of the construction techniques exemplified here do not require expensive facilities or unusual conditions for preparation, developments of this research field will be limited only by our imaginations.1][72][73][74] Therefore, we propose that by thought alone novel functionalities for mesoporous sensor nanoarchitectonics can be produced.
This work was partly supported by World Premier International Research Center Initiative (WPI Initiative), MEXT, Japan and Core Research for Evolutional Science and Technology (CREST) and Precursory Research for Embryonic Science and Technology (PRESTO) programs of Japan Science and Technology Agency (JST), Japan.

FIG. 7 .
FIG. 7. Preparation of hollow nanocubes of Prussian Blue (PB) analogue for selective QCM sensing and removal of Cs ion.