Artificial olfactory sensor technology that mimics the olfactory mechanism: a comprehensive review.

Artificial olfactory sensors that recognize patterns transmitted by olfactory receptors are emerging as a technology for monitoring volatile organic compounds. Advances in statistical processing methods and data processing technology have made it possible to classify patterns in sensor arrays. Moreover, biomimetic olfactory recognition sensors in the form of pattern recognition have been developed. Deep learning and artificial intelligence technologies have enabled the classification of pattern data from more sensor arrays, and improved artificial olfactory sensor technology is being developed with the introduction of artificial neural networks. An example of an artificial olfactory sensor is the electronic nose. It is an array of various types of sensors, such as metal oxides, electrochemical sensors, surface acoustic waves, quartz crystal microbalances, organic dyes, colorimetric sensors, conductive polymers, and mass spectrometers. It can be tailored depending on the operating environment and the performance requirements of the artificial olfactory sensor. This review compiles artificial olfactory sensor technology based on olfactory mechanisms. We introduce the mechanisms of artificial olfactory sensors and examples used in food quality and stability assessment, environmental monitoring, and diagnostics. Although current artificial olfactory sensor technology has several limitations and there is limited commercialization owing to reliability and standardization issues, there is considerable potential for developing this technology. Artificial olfactory sensors are expected to be widely used in advanced pattern recognition and learning technologies, along with advanced sensor technology in the future.

Recent Trends in Exhaled Breath Diagnosis Using an Artificial Olfactory System.

Artificial olfactory systems are needed in various fields that require real-time monitoring, such as healthcare. This review introduces cases of detection of specific volatile organic compounds (VOCs) in a patient's exhaled breath and discusses trends in disease diagnosis technology development using artificial olfactory technology that analyzes exhaled human breath. We briefly introduce algorithms that classify patterns of odors (VOC profiles) and describe artificial olfactory systems based on nanosensors. On the basis of recently published research results, we describe the development trend of artificial olfactory systems based on the pattern-recognition gas sensor array technology and the prospects of application of this technology to disease diagnostic devices. Medical technologies that enable early monitoring of health conditions and early diagnosis of diseases are crucial in modern healthcare. By regularly monitoring health status, diseases can be prevented or treated at an early stage, thus increasing the human survival rate and reducing the overall treatment costs. This review introduces several promising technical fields with the aim of developing technologies that can monitor health conditions and diagnose diseases early by analyzing exhaled human breath in real time.

Investigation of colorimetric biosensor array based on programable surface chemistry of M13 bacteriophage towards artificial nose for volatile organic compound detection: From basic properties of the biosensor to practical application.

Various threats such as explosives, drugs, environmental hormones, and spoiled food manifest themselves with the presence of volatile organic compounds (VOCs) in our environment. In order to recognize and respond to these threats early, the demand for highly sensitive and selective electronic noses is increasing. The M13 bacteriophage-based optoelectronic nose is an excellent candidate to meet all these requirements. However, the phage-based electronic nose is still in its infancy, and strategies that include a systematic approach and development are still essential. Here, we have integrated theoretical and experimental approaches to analyze the correlation between the surface chemistry of genetically engineered phage and the phage-based optoelectronic nose properties. The reactivity of the genetically engineered phage color film to some VOCs were quantitatively analyzed, and the correlation with the binding affinity value calculated by Density-functional theory (DFT) was compared. This demonstrates that phage color films have controllable reactivity through a genetic engineering. We have selected phages that are advantageous in distinguishing each VOCs in this work through hierarchical cluster analysis (HCA). The reason for this difference was verified through the optimized geometry calculated by DFT. Through this, it was confirmed that the tryptophan-based and the Histidine-based of genetically engineered phage film are important in distinguishing the VOCs (Y-hexanolactone, 2-isopropyl-4-methylthiazole, ethanol, acetone, ethyl acetate, and acetaldehyde) used in this work to evaluate the peach freshness quality. This was applied to the design of a field-applied phage-based optoelectronic nose and verified by measuring the freshness of the actual fruit.

Development of Two-Dimensional Nanomaterials Based Electrochemical Biosensors on Enhancing the Analysis of Food Toxicants.

In recent times, food safety has become a topic of debate as the foodborne diseases triggered by chemical and biological contaminants affect human health and the food industry's profits. Though conventional analytical instrumentation-based food sensors are available, the consumers did not appreciate them because of the drawbacks of complexity, greater number of analysis steps, expensive enzymes, and lack of portability. Hence, designing easy-to-use tests for the rapid analysis of food contaminants has become essential in the food industry. Under this context, electrochemical biosensors have received attention among researchers as they bear the advantages of operational simplicity, portability, stability, easy miniaturization, and low cost. Two-dimensional (2D) nanomaterials have a larger surface area to volume compared to other dimensional nanomaterials. Hence, researchers nowadays are inclined to develop 2D nanomaterials-based electrochemical biosensors to significantly improve the sensor's sensitivity, selectivity, and reproducibility while measuring the food toxicants. In the present review, we compile the contribution of 2D nanomaterials in electrochemical biosensors to test the food toxicants and discuss the future directions in the field. Further, we describe the types of food toxicity, methodologies quantifying food analytes, how the electrochemical food sensor works, and the general biomedical properties of 2D nanomaterials.

Hierarchical Cluster Analysis of Medical Chemicals Detected by a Bacteriophage-Based Colorimetric Sensor Array.

M13 bacteriophage-based colorimetric sensors, especially multi-array sensors, have been successfully demonstrated to be a powerful platform for detecting extremely small amounts of target molecules. Colorimetric sensors can be fabricated easily using self-assembly of genetically engineered M13 bacteriophage which incorporates peptide libraries on its surface. However, the ability to discriminate many types of target molecules is still required. In this work, we introduce a statistical method to efficiently analyze a huge amount of numerical results in order to classify various types of target molecules. To enhance the selectivity of M13 bacteriophage-based colorimetric sensors, a multi-array sensor system can be an appropriate platform. On this basis, a pattern-recognizing multi-array biosensor platform was fabricated by integrating three types of sensors in which genetically engineered M13 bacteriophages (wild-, RGD-, and EEEE-type) were utilized as a primary building block. This sensor system was used to analyze a pattern of color change caused by a reaction between the sensor array and external substances, followed by separating the specific target substances by means of hierarchical cluster analysis. The biosensor platform could detect drug contaminants such as hormone drugs (estrogen) and antibiotics. We expect that the proposed biosensor system could be used for the development of a first-analysis kit, which would be inexpensive and easy to supply and could be applied in monitoring the environment and health care.

Implementation of Combinatorial Genetic and Microenvironmental Engineering to Microbial-Based Field-Deployable Microbead Biosensors for Highly Sensitive and Remote Chemical Detection.

Bioreporters, microbial species genetically engineered to provide measurable signals in response to specific chemicals, have been widely investigated as sensors for biomedical and environmental monitoring. More specifically, the bioreporter encapsulated within a biocompatible material, such as a hydrogel that can provide a suitable microenvironment for its prolonged activity as well as efficient scalable production, has been viewed as a more broadly applicable mode of biosensors. In this study, alginate-based microbeads encapsulated with the bacterial bioreporter capable of expressing green fluorescence protein in response to nitro compounds (e.g., trinitrotoluene and dinitrotoluene) are developed as biosensors. To significantly enhance the sensitivity of the microbial-based microbead biosensors, "multifaceted" modification strategies are simultaneously employed: (1) multiple genetic modifications of the bioreporter, (2) tuning the physicomechanical properties of the encapsulating microbeads, (3) controlling the initial cell density within the microbeads, and (4) enrichment of nitro compounds inside microbeads via functional nanomaterials. These microbial and microenvironmental engineering approaches combine to significantly enhance the sensing capability, even allowing highly sensitive remote detection under a low-vapor phase. Thus, the strategy developed herein is expected to contribute to various cell-based biosensors.

Virus-Incorporated Biomimetic Nanocomposites for Tissue Regeneration.

Owing to the astonishing properties of non-harmful viruses, tissue regeneration using virus-based biomimetic materials has been an emerging trend recently. The selective peptide expression and enrichment of the desired peptide on the surface, monodispersion, self-assembly, and ease of genetic and chemical modification properties have allowed viruses to take a long stride in biomedical applications. Researchers have published many reviews so far describing unusual properties of virus-based nanoparticles, phage display, modification, and possible biomedical applications, including biosensors, bioimaging, tissue regeneration, and drug delivery, however the integration of the virus into different biomaterials for the application of tissue regeneration is not yet discussed in detail. This review will focus on various morphologies of virus-incorporated biomimetic nanocomposites in tissue regeneration and highlight the progress, challenges, and future directions in this area.

Experimental and numerical evaluation of a genetically engineered M13 bacteriophage with high sensitivity and selectivity for 2,4,6-trinitrotoluene.

Selective and sensitive detection of desired targets is very critical in sensor design. Here, we report a genetically engineered M13 bacteriophage-based sensor system evaluated by quantum mechanics (QM) calculations. Phage display is a facile way to develop the desired peptide sequences, but the resulting sequences can be imperfect peptides for binding of target molecules. A TNT binding peptide (WHW) carrying phage was self-assembled to fabricate thin films and tested for the sensitive and selective surface plasmon resonance-based detection of TNT molecules at the 500 femtomole level. SPR studies performed with the WHW peptide and control peptides (WAW, WHA, AHW) were well-matched with those of the QM calculations. Our combined method between phage engineering and QM calculation will significantly enhance our ability to design selective and sensitive sensors.

Improvement of High Affinity and Selectivity on Biosensors Using Genetically Engineered Phage by Binding Isotherm Screening.

The genetically engineered M13 bacteriophage (M13 phage), developed via directed evolutionary screening process, can improve the sensitivity of sensors because of its selective binding to a target material. Herein, we propose a screening method to develop a selective and sensitive bioreporter for toxic material based on genetically engineered M13 phage. The paraquat (PQ)-binding M13 phage, developed by directed evolution, was used. The binding affinities of the PQ-binding M13 phage to PQ and similar molecules were analyzed using isothermal titration calorimetry (ITC). Based on the isotherms measured by ITC, binding affinities were calculated using the one-site binding model. The binding affinity was 5.161 × 10-7 for PQ, and 3.043 × 10-7 for diquat (DQ). The isotherm and raw ITC data show that the PQ-binding M13 phage does not selectively bind to difenzoquat (DIF). The phage biofilter experiment confirmed the ability of PQ-binding M13 bacteriophage to bind PQ. The surface-enhanced Raman scattering (SERS) platform based on the bioreporter, PQ-binding M13 phage, exhibited 3.7 times the signal intensity as compared with the wild-type-M13-phage-coated platform.

Intermolecular distance measurement with TNT suppressor on the M13 bacteriophage-based Förster resonance energy transfer system.

An M13 bacteriophage-based Förster resonance energy transfer (FRET) system is developed to estimate intermolecular distance at the nanoscale using a complex of CdSSe/ZnS nanocrystal quantum dots, genetically engineered M13 bacteriophages labeled with fluorescein isothiocyanate and trinitrotoluene (TNT) as an inhibitor. In the absence of trinitrotoluene, it is observed that a significant spectral shift from blue to green occur, which represents efficient energy transfer through dipole-dipole coupling between donor and acceptor, or FRET-on mode. On the other hand, in the presence of trinitrotoluene, the energy transfer is suppressed, since the donor-to-acceptor intermolecular distance is detuned by the specific capturing of TNT by the M13 bacteriophage, denoted as FRET-off mode. These noble features are confirmed by changes in the fluorescence intensity and the fluorescence decay curve. TNT addition to our system results in reducing the total energy transfer efficiency considerably from 16.1% to 7.6% compared to that in the non-TNT condition, while the exciton decay rate is significantly enhanced. In particular, we confirm that the energy transfer efficiency satisfies the original intermolecular distance dependence of FRET. The relative donor-to-acceptor distance is changed from 70.03 Å to 80.61 Å by inclusion of TNT.

Self-Assembled Nanoporous Biofilms from Functionalized Nanofibrous M13 Bacteriophage.

Highly periodic and uniform nanostructures, based on a genetically engineered M13 bacteriophage, displayed unique properties at the nanoscale that have the potential for a variety of applications. In this work, we report a multilayer biofilm with self-assembled nanoporous surfaces involving a nanofiber-like genetically engineered 4E-type M13 bacteriophage, which was fabricated using a simple pulling method. The nanoporous surfaces were effectively formed by using the networking-like structural layers of the M13 bacteriophage during self-assembly. Therefore, an external template was not required. The actual M13 bacteriophage-based fabricated multilayered biofilm with porous nanostructures agreed well with experimental and simulation results. Pores formed in the final layer had a diameter of about 150⁻500 nm and a depth of about 15⁻30 nm. We outline a filter application for this multilayered biofilm that enables selected ions to be extracted from a sodium chloride solution. Here, we describe a simple, environmentally friendly, and inexpensive fabrication approach with large-scale production potential. The technique and the multi-layered biofilms produced may be applied to sensor, filter, plasmonics, and bio-mimetic fields.

Ternary Aligned Nanofibers of RGD Peptide-Displaying M13 Bacteriophage/PLGA/Graphene Oxide for Facilitated Myogenesis.

Recently, there have been tremendous efforts to develop the biofunctional scaffolds by incorporating various biochemical factors. In the present study, we fabricated poly(lactic-co-glycolic acid) (PLGA) nanofiber sheets decorated with graphene oxide (GO) and RGD peptide. The decoration of GO and RGD peptide was readily achieved by using RGD peptide-displaying M13 bacteriophage (RGD-M13 phage) and electrospinning. Furthermore, the aligned GO-decorated PLGA/RGD peptide (GO-PLGA/RGD) ternary nanofiber sheets were prepared by magnetic field-assisted electrospinning, and their potentials as bifunctional scaffolds for facilitating myogenesis were explored. We characterized the physicochemical and mechanical properties of the sheets by scanning electron microscopy, Raman spectroscopy, contact angle measurement, and tensile test. In addition, the C2C12 skeletal myoblasts were cultured on the aligned GO-PLGA/RGD nanofiber sheets, and their cellular behaviors, including initial attachment, proliferation and myogenic differentiation, were evaluated. Our results revealed that the GO-PLGA/RGD nanofiber sheets had suitable physicochemical and mechanical properties for supporting cell growth, and could significantly promote the spontaneous myogenic differentiation of C2C12 skeletal myoblasts. Moreover, it was revealed that the myogenic differentiation was further accelerated on the aligned GO-PLGA/RGD nanofiber sheets due to the synergistic effects of RGD peptide, GO and aligned nanofiber structure. Therefore, , it is suggested that the aligned GO-PLGA/RGD ternary nanofiber sheets are one of the most promising approaches for facilitating myogenesis and promoting skeletal tissue regeneration.

M13 Bacteriophage/Silver Nanowire Surface-Enhanced Raman Scattering Sensor for Sensitive and Selective Pesticide Detection.

A surface-enhanced Raman scattering (SERS) sensor comprising silver nanowires (AgNWs) and genetically engineered M13 bacteriophages expressing a tryptophan-histidine-tryptophan (WHW) peptide sequence (BPWHW) was fabricated by simple mixing of BPWHW and AgNW solutions, followed by vacuum filtration onto a glass-fiber filter paper (GFFP) membrane. The AgNWs stacked on the GFFP formed a high density of SERS-active hot spots at the points of nanowire intersections, and the surface-coated BPWHW functioned as a bioreceptor for selective pesticide detection. The BPWHW-functionalized AgNW (BPWHW/AgNW) sensor was characterized by scanning electron microscopy, confocal scanning fluorescence microscopy, atomic force microscopy, and Fourier transform infrared spectroscopy. The Raman signal enhancement and the selective pesticide SERS detection properties of the BPWHW/AgNW sensor were investigated in the presence of control substrates such as wild-type M13 bacteriophage-decorated AgNWs (BPWT/AgNW) and undecorated AgNWs (AgNW). The BPWHW/AgNW sensor exhibited a significantly higher capture capability for pesticides, especially paraquat (PQ), than the control SERS substrates, and it also showed a relatively higher selectivity for PQ than for other bipyridylium pesticides such as diquat and difenzoquat. Furthermore, as a field application test, PQ was detected on the surface of PQ-pretreated apple peels, and the results demonstrated the feasibility of using a paper-based SERS substrate for on-site residual pesticide detection. The developed M13 bacteriophage-functionalized AgNW SERS sensor might be applicable for the detection of various pesticides and chemicals through modification of the M13 bacteriophage surface peptide sequence.

Bioinspired M-13 bacteriophage-based photonic nose for differential cell recognition.

A bioinspired M-13 bacteriophage-based photonic nose was developed for differential cell recognition. The M-13 bacteriophage-based photonic nose exhibits characteristic color patterns when phage bundle nanostructures, which were genetically modified to selectively capture vapor phase molecules, are structurally deformed. We characterized the color patterns of the phage bundle nanostructure in response to cell proliferation via several biomarkers differentially produced by cells, including hydrazine, o-xylene, ethylbenzene, ethanol and toluene. A specific color enables the successful identification of different types of molecular and cellular species. Our sensing technique utilized the versatile M-13 bacteriophage as a building block for fabricating bioinspired photonic crystals, which enables ease of fabrication and tunable selectivity through genetic engineering. Our simple and versatile bioinspired photonic nose could have possible applications in sensors for human health and national security, food discrimination, environmental monitoring, and portable and wearable sensors.

Correction: Bioinspired M-13 bacteriophage-based photonic nose for differential cell recognition.

[This corrects the article DOI: 10.1039/C6SC02021F.].

Identification of Endocrine Disrupting Chemicals using a Virus-Based Colorimetric Sensor.

A simple and portable colorimetric sensor based on M13 bacteriophage (phage) was devised to identify a class of endocrine disrupting chemicals, including benzene, phthalate, and chlorobenzene derivatives. Arrays of structurally and genetically modified M13 bacteriophage were fabricated so as to produce a biomimetic colorimetric sensor, and color changes in the phage arrays in response to several benzene derivatives were characterized. The sensor was also used to classify phthalate and chlorobenzene derivatives as representatives of endocrine disrupting chemicals. The characteristic color patterns obtained on exposure to various benzene derivatives enabled similar chemical structures in the vapor phase to be classified. Our sensing approach based on the use of a genetically surface modified M13 bacteriophage offers a promising platform for portable, simple environmental monitors that could be extended for use in numerous application areas, including food monitoring, security monitoring, explosive risk assessment, and point of care testing.

Biomimetic self-templating optical structures fabricated by genetically engineered M13 bacteriophage.

Here, we describe a highly sensitive and selective surface plasmon resonance sensor system by utilizing self-assembly of genetically engineered M13 bacteriophage. About 2700 copies of genetically expressed peptide copies give superior selectivity and sensitivity to M13 phage-based SPR sensor. Furthermore, the sensitivity of the M13 phage-based SPR sensor was enhanced due to the aligning of receptor matrix in specific direction. Incorporation of specific binding peptide (His Pro Gln: HPQ) gives M13 bacteriophage high selectivity for the streptavidin. Our M13 phage-based SPR sensor takes advantage of simplicity of self-assembly compared with relatively complex photolithography techniques or chemical conjugations. Additionally, designed structure which is composed of functionalized M13 bacteriophage can simultaneously improve the sensitivity and selectivity of SPR sensor evidently. By taking advantages of the genetic engineering and self-assembly, we propose the simple method for fabricating novel M13 phage-based SPR sensor system which has a high sensitivity and high selectivity.

Virus based Full Colour Pixels using a Microheater.

Mimicking natural structures has been received considerable attentions, and there have been a few practical advances. Tremendous efforts based on a self-assembly technique have been contributed to the development of the novel photonic structures which are mimicking nature's inventions. We emulate the photonic structures from an origin of colour generation of mammalian skins and avian skin/feathers using M13 phage. The structures can be generated a full range of RGB colours that can be sensitively switched by temperature and substrate materials. Consequently, we developed an M13 phage-based temperature-dependent actively controllable colour pixels platform on a microheater chip. Given the simplicity of the fabrication process, the low voltage requirements and cycling stability, the virus colour pixels enable us to substitute for conventional colour pixels for the development of various implantable, wearable and flexible devices in future.

M13 Bacteriophage-Based Self-Assembly Structures and Their Functional Capabilities.

Controlling the assembly of basic structural building blocks in a systematic and orderly fashion is an emerging issue in various areas of science and engineering such as physics, chemistry, material science, biological engineering, and electrical engineering. The self-assembly technique, among many other kinds of ordering techniques, has several unique advantages and the M13 bacteriophage can be utilized as part of this technique. The M13 bacteriophage (Phage) can easily be modified genetically and chemically to demonstrate specific functions. This allows for its use as a template to determine the homogeneous distribution and percolated network structures of inorganic nanostructures under ambient conditions. Inexpensive and environmentally friendly synthesis can be achieved by using the M13 bacteriophage as a novel functional building block. Here, we discuss recent advances in the application of M13 bacteriophage self-assembly structures and the future of this technology.

Cell-Adhesive Matrices Composed of RGD Peptide-Displaying M13 Bacteriophage/Poly(lactic-co-glycolic acid) Nanofibers Beneficial to Myoblast Differentiation.

Recently, there has been considerable effort to develop suitable scaffolds for tissue engineering applications. Cell adhesion is a prerequisite for cells to survive. In nature, the extracellular matrix (ECM) plays this role. Therefore, an ideal scaffold should be structurally similar to the natural ECM and have biocompatibility and biodegradability. In addition, the scaffold should have biofunctionality, which provides the potent ability to enhance the cellular behaviors, such as adhesion, proliferation and differentiation. This study concentrates on fabricating cell-adhesive matrices composed of RGD peptide-displaying M13 bacteriophage (RGD-M13 phage) and poly(lactic-co-glycolic acid, PLGA) nanofibers. Long rod-shaped M13 bacteriophages are non-toxic and can express many desired proteins on their surface. A genetically engineered M13 phage was constructed to display RGD peptides on its surface. PLGA is a biodegradable polymer with excellent biocompatibility and suitable physicochemical property for adhesive matrices. In this study, RGD-M13 phage/PLGA hybrid nanofiber matrices were fabricated by electrospinning. The physicochemical properties of these matrices were characterized by scanning electron microscopy, atomic force microscopy, Raman spectroscopy, and contact angle measurement. In addition, the cellular behaviors, such as the initial attachment, proliferation and differentiation, were analyzed by a CCK-8 assay and immunofluorescence staining to evaluate the potential application of these matrices to tissue engineering scaffolds. The RGD-M13 phage/PLGA nanofiber matrices could enhance the cellular behaviors and promote the differentiation of C2C12 myoblasts. These results suggest that the RGD-M13 phage/PLGA nanofiber matrices are beneficial to myoblast differentiation and can serve as effective tissue engineering scaffolds.