Catechol biosensing using a nanostructured layer-by-layer film containing Cl-catechol 1,2-dioxygenase

Catechol sensor based on pristine and transition metal embedded holey graphyne: a first-principles density functional theory study

To develop a highly sensitive and selective biosensor for detecting noxious biomolecules from the environment, we examined catechol (Cc) adsorption in pristine and transition metal (TM = Sc, Cu, and Pd) embedded 2D holey graphyne (hGY) monolayers using the first-principles density functional theory method. The interaction between Cc and the pristine hGY is purely weak, and hence the response of the sensing device will be difficult to detect. Therefore, the TM doping strategy is adopted to improve the sensitivity. According to our findings, Sc binds strongly to the hGY monolayer, with a binding energy of -4.09 eV and a charge transfer of 1.89e from the valence orbitals of Sc to the C 2p orbitals. Later on, the Cc adsorption on the TM-embedded hGY was investigated. The interaction of Cc with the transition metal involves charge transfer from Cc to the metal d orbital. A large binding energy of -3.22 eV and a significant charge transfer of about 0.9e from the O 2p orbitals of Cc to the valence orbital of Sc suggest that the Sc embedded hGY monolayer is a good choice for the efficient sensing of Cc molecules. Furthermore, ab initio MD simulations confirmed the structural stability of the Sc + hGY system at room temperature. We strongly believe that this theoretical work will aid the experimentalists in designing and developing 2D semiconducting nanolayer-based biosensors for commercial purposes.

Organic micropollutants paracetamol and ibuprofen-toxicity, biodegradation, and genetic background of their utilization by bacteria

Currently, analgesics and nonsteroidal anti-inflammatory drugs (NSAIDs) are classified as one of the most emerging group of xenobiotics and have been detected in various natural matrices. Among them, monocyclic paracetamol and ibuprofen, widely used to treat mild and moderate pain are the most popular. Since long-term adverse effects of these xenobiotics and their biological and pharmacokinetic activity especially at environmentally relevant concentrations are better understood, degradation of such contaminants has become a major concern. Moreover, to date, conventional wastewater treatment plants (WWTPs) are not fully adapted to remove that kind of micropollutants. Bioremediation processes, which utilize bacterial strains with increased degradation abilities, seem to be a promising alternative to the chemical methods used so far. Nevertheless, despite the wide prevalence of paracetamol and ibuprofen in the environment, toxicity and mechanism of their microbial degradation as well as genetic background of these processes remain not fully characterized. In this review, we described the current state of knowledge about toxicity and biodegradation mechanisms of paracetamol and ibuprofen and provided bioinformatics analysis concerning the genetic bases of these xenobiotics decomposition.

Printed and flexible biosensor for antioxidants using interdigitated ink-jetted electrodes and gravure-deposited active layer

Printing techniques have been extensively used in the fabrication of organic electronic devices, such as light-emitting diodes and display backplanes. These techniques, in particular inkjet printing, are being employed for the localized dispensing of solutions containing biological molecules and cells, leading to the fabrication of bio-functional microarrays and biosensors. Here, we report the fabrication of an all-printed and flexible biosensor for antioxidants. Gold (Au) interdigitated electrodes (IDEs) with sub-100 µm features were directly inkjet-printed on plastic substrates using a nanoparticle-based ink. Conductivities as high as 5×10(6) S/m (12% of bulk Au) were attained after sintering was conducted at plastic-compatible 200 °C for 6 h. The enzyme Tyrosinase (Tyr) was used in the active layer of the biosensors, being innovatively deposited by large-area rotogravure printing. A tailor-made ink was studied, and the residual activity of the enzyme was 85% after additives incorporation, and 15.5% after gravure printing. Au IDEs were coated with gravure films of the Tyr-containing ink, and the biosensor was encapsulated with a cellulose acetate dip-coating film to avoid dissolution. The biosensor impedance magnitude increases linearly with the concentration of a model antioxidant, allowing for the construction of a calibration curve. Control experiments demonstrated the molecular recognition characteristic inferred by the enzyme. We found that the biosensor sensitivity and the limit of detection were, respectively, 5.68 Ω/µm and 200 µM. In conclusion, a disposable, light-weight, all-printed and flexible biosensor for antioxidants was successfully fabricated using fast and large-area printing techniques. This opens the door for the fabrication of technological products using roll-to-roll processes.

Enzyme nanoarchitectonics: organization and device application

Fabrication of ultrasmall functional machines and their integration within ultrasmall areas or volumes can be useful for creation of novel technologies. The ultimate goal of the development of ultrasmall machines and device systems is to construct functional structures where independent molecules operate as independent device components. To realize exotic functions, use of enzymes in device structures is an attractive solution because enzymes can be regarded as efficient machines possessing high reaction efficiencies and specificities and can operate even under ambient conditions. In this review, recent developments in enzyme immobilization for advanced functions including device applications are summarized from the viewpoint of micro/nano-level structural control, or nanoarchitectonics. Examples are roughly classified as organic soft matter, inorganic soft materials or integrated/organized media. Soft matter such as polymers and their hybrids provide a medium appropriate for entrapment and encapsulation of enzymes. In addition, self-immobilization based on self-assembly and array formation results in enzyme nanoarchitectures with soft functions. For the confinement of enzymes in nanospaces, hard inorganic mesoporous materials containing well-defined channels play an important role. Enzymes that are confined exhibit improved stability and controllable arrangement, which are useful for formation of functional relays and for their integration into artificial devices. Layer-by-layer assemblies as well as organized lipid assemblies such as Langmuir-Blodgett films are some of the best media for architecting controllable enzyme arrangements. The ultrathin forms of these films facilitate their connection with external devices such as electrodes and transistors. Artificial enzymes and enzyme-mimicking catalysts are finally briefly described as examples of enzyme functions involving non-biological materials. These systems may compensate for the drawbacks of natural enzymes, such as their instabilities under harsh conditions. We believe that enzymes and their mimics will be freely coupled, organized and integrated upon demand in near future technologies.

Dendrimers in layer-by-layer assemblies: synthesis and applications

We review the synthesis of dendrimer-containing layer-by-layer (LbL) assemblies and their applications, including biosensing, controlled drug release, and bio-imaging. Dendrimers can be built into LbL films and microcapsules by alternating deposition of dendrimers and counter polymers on the surface of flat substrates and colloidal microparticles through electrostatic bonding, hydrogen bonding, covalent bonding, and biological affinity. Dendrimer-containing LbL assemblies have been used to construct biosensors, in which electron transfer mediators and metal nanoparticles are often coupled with dendrimers. Enzymes have been successfully immobilized on the surface of electrochemical and optical transducers by forming enzyme/dendrimer LbL multilayers. In this way, high-performance enzyme sensors are fabricated. In addition, dendrimer LbL films and microcapsules are useful for constructing drug delivery systems because dendrimers bind drugs to form inclusion complexes or the dendrimer surface is covalently modified with drugs. Magnetic resonance imaging of cancer cells by iron oxide nanoparticles coated with dendrimer LbL film is also discussed.

Bending of layer-by-layer films driven by an external magnetic field

We report on optimized architectures containing layer-by-layer (LbL) films of natural rubber latex (NRL), carboxymethyl-chitosan (CMC) and magnetite (Fe₃O₄) nanoparticles (MNPs) deposited on flexible substrates, which could be easily bent by an external magnetic field. The mechanical response depended on the number of deposited layers and was explained semi-quantitatively with a fully atomistic model, where the LbL film was represented as superposing layers of hexagonal graphene-like atomic arrangements deposited on a stiffer substrate. The bending with no direct current or voltage being applied to a supramolecular structure containing biocompatible and antimicrobial materials represents a proof-of-principle experiment that is promising for tissue engineering applications in biomedicine.

Molecularly designed layer-by-layer (LbL) films to detect catechol using information visualization methods

The control of molecular architectures has been exploited in layer-by-layer (LbL) films deposited on Au interdigitated electrodes, thus forming an electronic tongue (e-tongue) system that reached an unprecedented high sensitivity (down to 10(-12) M) in detecting catechol. Such high sensitivity was made possible upon using units containing the enzyme tyrosinase, which interacted specifically with catechol, and by processing impedance spectroscopy data with information visualization methods. These latter methods, including the parallel coordinates technique, were also useful for identifying the major contributors to the high distinguishing ability toward catechol. Among several film architectures tested, the most efficient had a tyrosinase layer deposited atop LbL films of alternating layers of dioctadecyldimethylammonium bromide (DODAB) and 1,2-dipalmitoyl-sn-3-glycero-fosfo-rac-(1-glycerol) (DPPG), viz., (DODAB/DPPG)5/DODAB/Tyr. The latter represents a more suitable medium for immobilizing tyrosinase when compared to conventional polyelectrolytes. Furthermore, the distinction was more effective at low frequencies where double-layer effects on the film/liquid sample dominate the electrical response. Because the optimization of film architectures based on information visualization is completely generic, the approach presented here may be extended to designing architectures for other types of applications in addition to sensing and biosensing.

Toward the optimization of an e-tongue system using information visualization: a case study with perylene tetracarboxylic derivative films in the sensing units

The wide variety of molecular architectures used in sensors and biosensors and the large amount of data generated with some principles of detection have motivated the use of computational methods, such as information visualization techniques, not only to handle the data but also to optimize sensing performance. In this study, we combine projection techniques with micro-Raman scattering and atomic force microscopy (AFM) to address critical issues related to practical applications of electronic tongues (e-tongues) based on impedance spectroscopy. Experimentally, we used sensing units made with thin films of a perylene derivative (AzoPTCD acronym), coating Pt interdigitated electrodes, to detect CuCl(2) (Cu(2+)), methylene blue (MB), and saccharose in aqueous solutions, which were selected due to their distinct molecular sizes and ionic character in solution. The AzoPTCD films were deposited from monolayers to 120 nm via Langmuir-Blodgett (LB) and physical vapor deposition (PVD) techniques. Because the main aspects investigated were how the interdigitated electrodes are coated by thin films (architecture on e-tongue) and the film thickness, we decided to employ the same material for all sensing units. The capacitance data were projected into a 2D plot using the force scheme method, from which we could infer that at low analyte concentrations the electrical response of the units was determined by the film thickness. Concentrations at 10 μM or higher could be distinguished with thinner films--tens of nanometers at most--which could withstand the impedance measurements, and without causing significant changes in the Raman signal for the AzoPTCD film-forming molecules. The sensitivity to the analytes appears to be related to adsorption on the film surface, as inferred from Raman spectroscopy data using MB as analyte and from the multidimensional projections. The analysis of the results presented may serve as a new route to select materials and molecular architectures for novel sensors and biosensors, in addition to suggesting ways to unravel the mechanisms behind the high sensitivity obtained in various sensors.

Optimization of 2,3-dihydroxybiphenyl 1,2-dioxygenase expression and its application for biosensor

In this study, two statistical experimental designs, Plackett-Burman design (PBD) and response surface methodology (RSM), were employed to enhance the expression of 2,3-dihydroxybiphenyl 1,2-dioxygenase (BphC_LA-4), which was subsequently used for the construction of catechol biosensor. Ten important factors were evaluated by PBD, and four significant parameters were then optimized by RSM. Under the favorable fermentation conditions, the maximal specific activity of BphC_LA-4 was about 0.58U/mg with catechol as substrate. Meanwhile, homology modeling and molecular docking were utilized to help understand the interaction between BphC_LA-4 and catecholic substrates, which illustrated that BphC_LA-4 presented lower binding affinity towards 4-methylcatechol in comparison with 3-methylcatechol and catechol. Interestingly, the BphC_LA-4 enzyme electrode prepared by SiO2 sol-gel showed good response to all these three catecholic compounds. The differences of selectivity to 4-methylcatechol between free and immobilized enzyme implied that the introduction of electro-catalysis might have an effect on the enzyme-catalysis process.

Recent advances in electronic tongues

This minireview describes the main developments of electronic tongues (e-tongues) and taste sensors in recent years, with a summary of the principles of detection and materials used in the sensing units. E-tongues are sensor arrays capable of distinguishing very similar liquids employing the concept of global selectivity, where the difference in the electrical response of different materials serves as a fingerprint for the analysed sample. They have been widely used for the analysis of wines, fruit juices, coffee, milk and beverages, in addition to the detection of trace amounts of impurities or pollutants in waters. Among the various principles of detection, electrochemical measurements and impedance spectroscopy are the most prominent. With regard to the materials for the sensing units, in most cases use is made of ultrathin films produced in a layer-by-layer fashion to yield higher sensitivity with the advantage of control of the film molecular architecture. The concept of e-tongues has been extended to biosensing by using sensing units capable of molecular recognition, as in films with immobilized antigens or enzymes with specific recognition for clinical diagnosis. Because the identification of samples is basically a classification task, there has been a trend to use artificial intelligence and information visualization methods to enhance the performance of e-tongues.

Antimicrobial peptides from Phyllomedusa frogs: from biomolecular diversity to potential nanotechnologic medical applications

Screening for new bioactive peptides in South American anurans has been pioneered in frogs of the genus Phyllomedusa. All frogs of this genus have venomous skin secretions, i.e., a complex mixture of bioactive peptides against potential predators and pathogens that presumably evolved in a scenario of predator-prey interaction and defense against microbial invasion. For every new anuran species studied new peptides are found, with homologies to hormones, neurotransmitters, antimicrobials, and several other peptides with unknown biological activity. From Vittorio Erspamer findings, this genus has been reported as a "treasure store" of bioactive peptides, and several groups focus their research on these species. From 1966 to 2009, more than 200 peptide sequences from different Phyllomedusa species were deposited in UniProt and other databases. During the last decade, the emergence of high-throughput molecular technologies involving de novo peptide sequencing via tandem mass spectrometry, cDNA cloning, pharmacological screening, and surface plasmon resonance applied to peptide discovery, led to fast structural data acquisition and the generation of peptide molecular libraries. Research groups on bioactive peptides in Brazil using these new technologies, accounted for the exponential increase of new molecules described in the last decade, much higher than in any previous decades. Recently, these secretions were also reported as a rich source of multiple antimicrobial peptides effective against multidrug resistant strains of bacteria, fungi, protozoa, and virus, providing instructive lessons for the development of new and more efficient nanotechnological-based therapies for infectious diseases treatment. Therefore, novel drugs arising from the identification and analysis of bioactive peptides from South American anuran biodiversity have a promising future role on nanobiotechnology.

Layer-by-layer technique as a new approach to produce nanostructured films containing phospholipids as transducers in sensing applications

Phospholipids are widely used as mimetic systems to exploit interactions involving biological membranes and pharmacological drugs. In this work, the layer-by-layer (LbL) technique was used as a new approach to produce multilayered thin films containing biological phospholipids applied as transducers onto Pt interdigitated electrodes forming sensing units of an electronic tongue system. Low concentrations (nM level) of a phenothiazine compound were detected through impedance spectroscopy. Both negative 1,2-dipalmitoyl-sn-3-glycero-[phosphor-rac-(1-glycerol)] (DPPG) and zwitterionic l-alpha-1,2-dipalmitoyl-sn-3-glycero-phosphatidylcholine (DPPC) phospholipids were used to produce the LbL films, whose molecular architecture was monitored combining spectroscopy and microscopy at micro and nanoscales. The sensor array was complemented by Langmuir-Blodgett (LB) monolayers of DPPG and DPPC deposited onto Pt interdigitated electrodes as well. It was found that the distinct molecular architecture presented by both LbL and LB films plays a key role on the sensitivity of the sensor array with the importance of the LbL films being demonstrated by principal component analysis (PCA).

Leishmanicidal activity and immobilization of dermaseptin 01 antimicrobial peptides in ultrathin films for nanomedicine applications

Antimicrobial peptides (AMPs) are essential for the innate immune system of eukaryotes, imparting protection against pathogens and their proliferation in host organisms. The recent interest in AMPs as active materials in bionanostructures is due to the properties shown by these biological molecules, such as the presence of an alpha-helix structure and distribution of positive charges along the chain. In this study the antimicrobial peptide dermaseptin 01 (DS 01), from the skin secretion of Phyllomedusa hypochondrialis frogs was immobilized in nanostructured layered films in conjunction with nickel tetrasulfonated phthalocyanines. The leishmanicidal activity of DS 01 was confirmed using kinetic essays, in which DS 01 promoted death of all metacyclic promastigote cells in 45 minutes. Surprisingly, the immobilized DS 01 molecules displayed electroactivity, as revealed by electrochemical experiments, in which an oxidation peak at about 0.61 V was observed for a DS 01 monolayer deposited on top of a conductive electrode. Such electroactivity was used to investigate the sensing abilities of the nanostructured films toward Leishmania. We observed an increase in the oxidation current as a function of number of Leishmania cells in the electrolytic solution at concentrations down to 10(3) cells/mL. The latter is indicative that the use of AMPs immobilized in electroactive nanostructured films may be of interest for applications in the pharmaceutical industry and diagnosis.

FROM THE CLINICAL EDITOR

The recent interest in Antimicrobial peptides (AMPs) as active materials in bionanostructures is due to the properties shown by these biological molecules. Leishmanicidal activity of a particular AMP is demonstrated in this paper.

Electrochemically enabled polyelectrolyte multilayer devices: from fuel cells to sensors

With an ever-increasing need for thin, flexible and functional materials in electrochemical systems, the layer-by-layer (LbL) technique provides a simple and affordable route in creating new, active electrodes and electrolytes. The LbL technique, which is based upon the alternate adsorption of oppositely charged species from aqueous solution, possesses unprecedented control of materials selection ( polyelectrolytes, clays, nanoparticles, proteins), materials properties ( conductivity, glass-transition temperature) and architecture ( blends, stratified-layers, pores). These advantages make LbL assemblies excellent candidates for use in proton-exchange membrane and direct methanol fuel-cells, batteries, electrochromic devices, solar cells, and sensors. This review addresses the design of LbL films for electrochemical systems and recent progress.

Using Capacitance Measurements as the Detection Method in Antigen-Containing Layer-by-Layer Films for Biosensing

The layer-by-layer technique is employed here to immobilize antigen-containing liposomes, so-called proteoliposomes, onto Au-interdigitated substrates, which are capable of molecular recognition of anti-pasteurellosis antibodies. Detection was carried out using a novel strategy entirely based upon capacitance measurements, and to enhance sensitivity, we combine the response of three different sensing units in a similar procedure used for taste sensors. With the three-electrode array immunoglobulin G (IgG) against pasteurellosis is detected at concentrations as low as nanograms per milliliter. Furthermore, because of the molecular recognition capability, a distinction can be made between specific and nonspecific IgG. The concepts behind the biosensors reported here may have a large impact for clinical tests, as the procedures to detect the antibody take only a few minutes and the biosensors are relatively low cost.