Chiral Biosensor Research Articles

Engineering DNAzyme cyclic amplification integrated dual-signal chiral sensing system for specific recognition of histidine enantiomers

A novel label-free dual-signal amplifying “on-off-on” electrochemical biosensor has been designed for specific recognition of histidine (His) enantiomers. The remarkable dual-signal is provided by engineering His-dependent DNAzyme and the Fe3O4 nanoparticles attached reduced graphene oxide nanocomposite (Fe3O4@rGO) as enzymatically magnified chiral selector and electroactive indicator, respectively. In this strategy, L-histidine (L-His) cyclically catalyzes the cleavage of the substrate sequences, leading to the release of rich G-quadruplex and enzymatic sequences. The released enzymatic sequences sequentially trigger the additional cleavage cycle, the G-quadruplex forming sequences associate with hemin to form G-quadruplex/hemin structures, which act as label-free NADH oxidase to generate significantly amplified current for sensitive detection of L-His. Whereas no obvious response is observed after the DNAzyme cascade assay reacted with D-His. And the proposed chiral biosensor based on dual outputs “AND” logic gate has been constructed to facilitate the application. Combined the merits of His-dependent DNAzyme amplifying electrochemical response and the dual-signal generated by the new electroactive materials, the developed assay for the detection of His enantiomers demonstrate excellent selectivity and sensitivity. This can promote the promising applications of the versatile DNAzyme-based biosensing concept in chiral recognition of other amino acids.

Novel potential and current type chiral amino acids biosensor based on L/D-handed double helix carbon nanotubes@polypyrrole@Au nanoparticles@L/D-cysteine

Novel chiral amino acids biosensor based on both potential difference and current ratio simultaneously was first established by employing left/right-handed double helix carbon nanotubes (L/D-DHCNT) with chiral structure as substrate material, and by self-assembly anchoring L/D-cysteine (L/D-Cys) on the surface of the left/right-handed double helix carbon nanotubes@Polypyrrole@Au nanoparticles nanocomposites (L/D-DHCNT@PPy@AuNPs). In this work, L/D-DHCNT@PPy@AuNPs@L/D-Cys was successfully constructed via a facile and environment-friendly process. Interestingly, in order to obtain highly dispersed AuNPs deposited on L/D-DHCNT, polypyrrole polymerized from pyrrole acts as a locating agent. Owing to the combination of unique performance of the L/D-Cys and L/D-DHCNT with chiral structure, and PPy and AuNPs with outstanding conductivity, an extremely efficient electrochemical chiral biosensing system was constructed that exhibited enhanced conductivity, sensitivity and chiral recognition capacity for tyrosine (Tyr), tryptophan (Trp) and glutamic acids (Glu) enantiomers. Utilizing both the potential difference and current ratio signal to commendably realize the electrochemical recognition and quantitative determination of amino acid enantiomers in their racemic solution. In addition, achieving the detection of Tyr in tablet samples by fabricated ultra-efficient electrochemical chiral biosensing system. Therefore, L/D-DHCNT@PPy@AuNPs@L/D-Cys as novel and ultrasensitive chiral biosensing system possesses the capability of chiral recognition of amino acid enantiomers, and it opens up the potential application of L/D-DHCNT@PPy@AuNPs@L/D-Cys in the field of chiral biosensors.

Tunable circular dichroism of bilayer b-type chiral nanostructures

Circular dichroism (CD) of chiral molecules are key to medicine detection, optoelectronic devices and chiral biosensors. However, the CD effects of natural chiral molecules are weak that prevents their wide applications. Chiral plasmonic nanostructures have been demonstrated as an effective way to enhance CD effects of natural molecules due to the localized enhanced electromagnetic field and the high contrast in chiroptical response to left- and right-handed circular polarized light. Here we proposed a 3D plasmonic chiral platform consisting of bilayer b-shape nanoelements and investigated their tunable CD effects through rotating the upper layer b-elements. Near-field analysis based on Born–Kuhn model had been proposed to explain the mechanism of the tunable CD effects. Results demonstrated that a maximum CD signal was achieved with the 3D chiral nanostructure supporting bonding and antibonding plasmonic modes under left- and right-handed circular polarized light, respectively. While the smallest CD was for the nanostructure only supporting one mode (antibonding mode) under circular polarized light. The tunable CD effects of the bilayer b-type nanostructures is beneficial for chiral optical switches and high-sensitivity chiral biosensors.

Artificial Chiral Probes and Bioapplications.

The development of artificial chiral architectures, especially chiral inorganic nanostructures, has greatly promoted research into chirality in nanoscience. The nanoscale chirality of artificial chiral nanostructures offers many new application opportunities, including chiral catalysis, asymmetric synthesis, chiral biosensing, and others that may not be allowed by natural chiral molecules. Herein, the progress achieved during the past decade in chirality-associated biological applications (biosensing, biolabeling, and bioimaging) combined with individual chiral nanostructures (such as chiral semiconductor nanoparticles and chiral metal nanoparticles) or chiral assemblies is discussed.

Chiral Shell Core-Satellite Nanostructures for Ultrasensitive Detection of Mycotoxin.

Herein, the design of a DNA-based chiral biosensor is described utilizing the self-assembly of shell core-gold (Au) satellite nanostructures for the detection of mycotoxin, ochratoxin A (OTA). The assembly of core-satellite nanostructures based on OTA-aptamer binding exhibits a strong chiral signal with an intense circular dichroism (CD) peak. The integrity of the assembly of core-satellite nanostructures is limited to some extent in the presence of different levels of OTA. Correspondingly, the chiral intensity of assembly is weakened with increasing OTA concentrations, allowing quantitative determination of the target. The developed chiral sensor shows an excellent linear relationship between the CD signal and concentrations of OTA in the range of 0.1-5 pg mL-1 with a limit of detection as low as 0.037 pg mL-1 . The effectiveness of the biosensor in a sample of red wine is verified and a good recovery rate is obtained. These results suggest that the strategy has great potential for practical application.

Novel potential type electrochemical chiral recognition biosensor for amino acid

Novel potential type electrochemical chiral biosensing system with unique capability of distinguishing and quantitating of tyrosine (Tyr) enantiomers by L-cysteic acid and left-handed chiral carbonaceous nanotubes (L-CCNT) modified glassy carbon electrode (L-Cys/L-CCNT/GCE) was first developed. The effect of sweep cycles of L-Cys and the kinds of L-CCNT on electrochemical chiral biosensing performance of L-Cys/L-CCNT/GCE were investigated. The electrochemical identification and quantitative determination of L- and D-tyrosine in their mixed solution were successfully achieved based on the different oxidation potential signals. The chiral structure of L-CCNT, the aromatic ring of Tyr, and also the intermolecular hydrogen bond between cysteic acid (CyA) and Tyr could possibly produce the difference in the free energy, which reflects as potential difference of L- and D-tyrosine. A good linear relationship between the potential, current, and different concentration ratios of L- and D-Tyr was obtained. Our present work realizes the simultaneous detection of Tyr enantiomers in their mixed solution based on the different potential signals, and it is of far-reaching significance in real electrochemical chiral biosensor study.

Betamethasone-based chiral electrochemical sensor coupled to chemometric methods for determination of mandelic acid enantiomers.

A chiral biosensing platform was developed using betamethasone (BMZ) as chiral recognition element through multilayered electrochemical deposition of BMZ, overoxidized polypyrrole, and nanosheets of graphene (OPPy-BMZ/GR), for enantio-recognition of mandelic acid (MA) enantiomers. The deposited film was characterized by scanning electron microscopy, differential pulse voltammetry, cyclic voltammetry, and electrochemical impedance spectroscopy. It was shown that the chiral sensing platform can discriminate R- and S-MA differential pulse voltammetry signals, at the voltages of 1.35 and 1.33V (vs Ag/AgCl), respectively. To tackle the problem of highly overlapping peaks of these enantiomers, the partial least squares (PLS) regression and genetic algorithm-PLS (GA-PLS) were used for simultaneous quantification of MA enantiomers. Generally, variable selection by genetic algorithm provided an improvement in prediction results when compared to full-voltammogram PLS. Good analytical performances were obtained despite the inherent complexity of the simultaneous determination.

Numerical study of tunable enhanced chirality in multilayer stack achiral phase-change metamaterials.

We numerically demonstrate a multiband circular dichroism (CD) by tilting achiral metamaterials (MMs) composed of an elliptical nanoholes array (ENA) penetrating through metal/ phase-change material (PCM) /metal multilayer stack, with respect to the incident light. The CD spectrum can be actively tuned across a wide range from the near-infrared (NIR) to mid-infrared (MIR) regime by transiting the state of the PCM (Ge2Sb2Te5) from amorphous to crystalline. Thus, it can switch on/off a multiband chiroptical response in the infrared region. Our simulation also elucidates that the achiral multilayer stack MMs, which have strong magnetic resonances, can enhance the optical chirality inside the elliptical apertures for both amorphous and crystalline states. The switching of the enhanced chirality may pave the way to manipulate electromagnetic waves, such as tunable circular polarizers, chiroptical spectroscopy, and chiral biosensors.

Ultrabroadband Optical Superchirality in a 3D Stacked‐Patch Plasmonic Metamaterial Designed by Two‐Step Glancing Angle Deposition

Low‐cost and large‐scale fabrication of 3D chiral metamaterials is highly desired for potential applications such as nanophotonics devices and chiral biosensors. One of the promising fabrication methods is to use glancing angle deposition (GLAD) of metal on self‐assembled dielectric microsphere array. However, structural handedness varies locally due to long‐range disorder of the array and therefore large‐scale realization of the same handedness is impossible. Here, using symmetry considerations a two‐step GLAD process is proposed to eliminate this longstanding problem. In the proposed scheme, the unavoidable long‐range disorder gives rise to microscale domains of the same handedness but of slightly different structural geometries and ultimately contributes to a broad‐band response. Experimentally, a record‐breaking superchiral response of circular dichroism signal of ≈11° is demonstrated and an average polarization rotation angle of 27° in the visible region on ≈1 cm2 sample is observed. Computer‐aided geometric reconstruction with experimental parameters unambiguously reveal the presence of strong structural anisotropy and chirality in the prepared stacked‐patch plasmonic chiral metamaterial; microscopic spectral analyses combined with full‐wave electromagnetic simulations coherently provide deeper insights into the measured circular dichroism and optical activity. The observed chiroptical response can also be flexibly controlled by adjusting the deposition parameters for various potential applications.

Scalable Fabrication of Quasi-Three-Dimensional Chiral Plasmonic Oligomers Based on Stepwise Colloid Sphere Lithography Technology.

We report a simple and scalable method for the fabrication of spiral-type chiral plasmonic oligomers based on the stepwise colloid sphere lithography technology. Through carefully adjusting the azimuthal angle Φ of polystyrene (PS) sphere array monolayer and the deposition thickness kn, the chiral plasmonic oligomers composed of four achiral particles can be successfully fabricated on a desired substrate. And their chiral sign, i.e., left-hand or right-hand, is dependent on the anticlockwise or clockwise deposition sequence of the achiral particles. The measured results show a large chiroptical resonance in the visible region, and this resonance can be easily adjusted by using different sizes of PS spheres. Our in-depth theoretical and experimental researches further reveal that the obtained chiral plasmonic oligomers are indeed a kind of quasi-three-dimensional chiral nanostructures, which own a three-dimensional geometrical morphology, but with nonreciprocity chiroptical effect. The ease and scalability (>1 cm2) of the fabrication method make chiral plasmonic oligomers promising candidates for many applications, such as chiral biosensor and catalysis.

Electron Energy Loss Spectroscopy of a Chiral Plasmonic Structure

A detailed analysis of the plasmonic excitations within a nanopatterned gold chiral biosensor element, measured by scanning transmission electron microscopy electron energy loss spectroscopy, is presented. We discuss aspects of data acquisition, processing, analysis and simulation. The localised surface plasmonic resonance modes in the structure are extracted using non-negative matrix factorisation and we use simulations to correlate notable deviations from the idealised spectrum to nanometric fabrication imperfections. The methodology presented has wide applicability to a variety of metamaterials.

Enhanced Optical Chirality through Locally Excited Surface Plasmon Polaritons

The possibility to enhance chiral light-matter interactions through plasmonic nanostructures provides entirely new opportunities for greatly improving the detection limits of chiroptical spectroscopies down to the single molecule level. The most pronounced of these chiral interactions occur in the ultraviolet (UV) range of the electromagnetic spectrum, which is difficult to access with conventional localized plasmon resonance based sensors. Although Surface Plasmon Polaritons (SPPs) on noble metal films can sustain resonances in the desired spectral range, their transverse magnetic nature has been an obstacle for enhancing chiroptical effects. Here we demonstrate, both analytically and numerically, that SPPs excited by near-field sources can exhibit rich and non-trivial chiral characteristics. In particular, we show that the excitation of SPPs by a chiral source not only results in a locally enhanced optical chirality but also achieves manifold enhancement of net optical chirality. Our finding that SPPs facilitate a plasmonic enhancement of optical chirality in the UV part of the spectrum is of great interest in chiral bio-sensing.

Plasmonically Enhanced Chiral Optical Fields and Forces in Achiral Split Ring Resonators

The two enantiomers (mirror images) of a biomolecule can show drastically different behaviors, requiring the development of sensitive approaches for their identification and separation. Plasmonic nanostructures have shown promise for enhancing the sensitivities of chiral spectroscopies, but the generation of chiral near fields with a specific handedness in the spatial domain surrounding the plasmonic structures remains a challenge. Here we demonstrate that achiral bianisotropic structures, which couple the electric and magnetic fields, can achieve high enhancements of optical chirality in an extended spatial region. Magneto-electric coupling in such structures facilitates electrically excited magnetic resonances in the near IR and optical regimes, which in turn can result in highly enhanced optical chirality in an extended region of space. We apply this concept to achiral double split ring resonators (DSRRs) and demonstrate their potential in generating enhanced chiral fields and forces. Also, the behavior of optical chirality density gradient and chirality flux in such structures is examined, and it is shown that plasmonically generated chiral forces may pave the way to a new class of chiral biosensors.

Enantioselective discrimination of l-/d-phenylalanine by bovine serum albumin and gold nanoparticles modified glassy carbon electrode

A new chiral biosensor able to discriminate and detect phenylalanine (Phe) enantiomers was fabricated by immobilizing bovine serum albumin (BSA) on gold-nanoparticle-modified glassy carbon electrodes.

Electrochemical Sensing for Naproxen Enantiomers Using Biofunctionalized Reduced Graphene Oxide Nanosheets

A chiral platform was designed for enantioselective recognition of naproxen (Nap) enantiomers using BSA biofunctionalized nanosheets of Toluidin blue O (TBO) and reduced graphene oxide (rGO) on the glassy carbon electrode. The novel TBO@rGO nanosheets acting as a supporter for the chiral selector (BSA) and electrochemical signal indicator had plenty of advantages, which were presented and explored via ultraviolet-visible (UV-vis) spectroscopy, scanning electron microscope (SEM) and electrochemical method. Kinetics showed the chiral platform had good redox signal and fast electron transfer. Under optimal conditions, much larger signal discrepancy was obtained after the chiral interface interacted with r-Nap, and a linear electrochemical response to Nap enantiomers was obtained from 5.0 × 10−4 mol L−1 to 5.0 × 10−3 mol L−1 with a low detection limit of 3.3 × 10−7 mol L−1. Meanwhile, quartz crystal microbalance (QCM) for the interactions between BSA and Nap enantiomers further confirmed that r-Nap had a higher affinity with BSA. Furthermore, this simple chiral biosensor with excellent sensitivity and high stability is very expected to have more application in enantioselective recognition.

Voltammetric discrimination of mandelic acid enantiomers

We report a novel electrochemical biosensor for direct discrimination of d- and l-mandelic acid (d- and l-MA) in aqueous medium. The glassy carbon electrode (GCE) surface was modified with reduced graphene oxide (rGO) and γ-globulin (GLOB). Electrochemical characterization of the modified electrodes was investigated by cyclic voltammetry and electrochemical impedance spectroscopy. The modified electrode surfaces were also characterized by scanning electron microscopy. Electrochemical response of the prepared electrode (GCE/rGO/GLOB) for discrimination of d- and l-MA enantiomers was investigated by cyclic voltammetry and was compared with bare GCE in the concentration range of 2 to 10mM. Whereas the bare GCE showed no electrochemical response for the MA enantiomers, the GCE/rGO/GLOB electrode exhibited direct and selective discrimination with different oxidation potential values of 1.47 and 1.71V and weak reduction peaks at potential values of −1.37 and −1.48V, respectively. In addition, electrochemical performance of the modified electrode was investigated in mixed solution of d- and l-MA. The results show that the produced electrode can be used as electrochemical chiral biosensor for MA.

The application of thionine–graphene nanocomposite in chiral sensing for Tryptophan enantiomers

The thionine–graphene (THi–GR, positively charged) nanocomposite was successfully synthesized as a good biocompatible matrix for ds-DNA which acted as a chiral selector to construct an electrochemical chiral biosensor for Tryptophan (Trp) enantiomers sensing with the assistance of Cu(II). The nano-bionic interface was constructed as follows: Firstly, the nanocomposite was dropped on the surface of glassy carbon electrode (GCE), and then ds-DNA (negatively charged) was immobilized onto the nanocomposite film via the opposite-charged adsorption techniques. This biofunctionalized nanocomposite was characterized with scanning electron microscopy (SEM), ultraviolet–visible (UV–vis) spectrometry and cyclic voltammetry (CV). The chiral biosensor was employed to study the recognition effect between ds-DNA and Trp enantiomers by CV. The results show that larger electrochemical response was obtained from l-Trp when Cu(II) was present, indicating this strategy could be employed to enantioselectively recognize Trp enantiomers. Under optimum conditions, the chiral biosensor exhibited a good linear response to Trp enantiomers in the range of the concentration of [Cu(II)(Trp)2] from 5.0×10−4 to 2.5mM with a low limit of detection of 0.17μM (S/N=3). The binding constant was calculated to be 2.97×103M−1 for [Cu(II)(l-Trp)2] and 2.50×102M−1 for [Cu(II)(d-Trp)2].

A reagentless enantioselective sensor for tryptophan enantiomers via nanohybrid matrices

A reagentless method for the selective electrochemical discrimination of tryptophan (Trp) enantiomers has been developed by means of adsorbing human serum albumin (HSA) onto a methylene blue–multi-wall carbon nanotubes nanohybrid (MB–MWNTs) modified glassy carbon electrode (HSA/MB–MWNT/GCE). Cyclic voltammetry (CV) was employed to monitor the immobilization processes and the electrochemical behavior of the Trp enantiomers on the HSA/MB–MWNT/GCE. It was found that the newly developed electrode exhibited different interactions toward the Trp enantiomers, with a stronger binding effect obtained between HSA and L-Trp. The linear range of the biosensor was investigated from 1.0 × 10−1 to 1.0 × 10−8 mol L−1 with a detection limit of 3.3 × 10−9 mol L−1. In addition, the values of the enantioselectivity coefficient (α) and the association constant (k) were calculated. This work appears to provide a reference for the development of a reagentless electrochemical chiral biosensor and improves understanding of the high selectivity between biological molecules and chiral amino acids.

Reagentless Biosensor Using for Stereospecific Interaction between γ-globulin and N-isobutyryl-cysteine

In the present study, a novel approach was designed to construct a reagentless chiral biosensor for highly selective recognition of N-isobutyryl-cysteine enantiomers. The reduced-graphene oxide sheets (rGO) and thionine (TH) were firstly stepwisely synthesized onto modified glassy carbon electrode using glutaraldehyde as a bifunctional reagent, and γ-globulin was adsorbed on the electrode surface as a chiral selector. TH-rGO with excellent redox electrochemical activities brought in more redox probes for chiral recogniton, which could improve the sensitivity of the biosensor. Good reproducibility and sufficient stability were obtained with the advantages of TH-rGO and glutaraldehyde reagent. Moreover, the proposed biosensor showed an obviously decreased current peak after adsorption of N-isobutyryl-L-cysteine isomer. As compared with penicillamine or cysteine enantiomers, the current biosensor showed good enantioselectivity for sensing N-isobutyryl-cysteine enantiomers.

Enantioselective recognition of mandelic acid based on γ-globulin modified glassy carbon electrode

A new chiral biosensor has been fabricated by immobilizing γ-globulin on gold nanoparticles modified glassy carbon electrodes, which could recognize and detect mandelic acid (MA) enantiomers. Differential pulse voltammetry, quartz crystal microbalance, ultraviolet–visible spectroscopy, and atomic force microscopy were used to characterize the enantioselectivity. The results exhibited that γ-globulin modified electrode could enantioselectively recognize MA enantiomers, and larger response signals were obtained from R-MA. The factors influencing the performance of the resulting biosensor were investigated. The enantiomeric composition of R- and S-MA enantiomer mixtures could be determined by measuring the current responses of the sample. The developed electrodes have the advantages of simple preparation, good stability, and rapid detection.