Use of liquid crystal to study the interactions of alkyl polyglycosides with gelatin and bovine serum albumin

In this study, liquid crystal (LC) was used to study the interactions of alkyl polyglycosides (APG) with gelatin and bovine serum albumin (BSA) at the LC-aqueous interface. The LC easily undergo an orientational transition from a homeotropic to a planar state after proteins were in contact to the LCaqueous interface decorated with APG, thus inducing an optical change from dark to bright. The optical image analysis reveals that the rearrangement rate of APG monolayer is tightly dependent on the concentration and chemical structure of the protein of interest. For example, the rearrangement rate of APG monolayer increases with an increasing gelatin concentration. We also find that the chemical structure of the proteins has a significant impact on the difference in the growth behavior of bright domains in LC.     

Dynamic imaging of enzymatic events at polyelectrolyte-disrupted phospholipid membranes using liquid crystals

In this study, we employed a simple liquid crystal (LC)-based system to dynamically image enzymatic events at the aqueous/LC interface decorated with polyelectrolyte-disrupted phospholipid membranes. Since polyelectrolytes were shown to disrupt the arrangement of the self-assembled phospholipid monolayer and induced a dark-to-bright shift in the optical response of LCs that support the phospholipid membrane, we observed that the transfer of an aqueous solution of protease onto the polyelectrolyte-disrupted phospholipid membrane resulted in a gradual recovery of the optical response of LCs from bright to dark appearance. Due to the enzymatic event that occurs at the aqueous/LC interface, the generated polyelectrolyte fragments desorbed from the interface to the bulk solution. This led to the restoration of the disrupted phospholipid monolayer, which resulted in recovery of the optical response. These results suggest that the polyelectrolyte-decorated membrane-supported LCs could be potentially used to examine a range of biological interactions that involve polyelectrolytes. Furthermore, the LC-based system holds great promise for label-free and real-time investigation and detection of biomolecular interactions coupled to membrane disruption and restoration, which might have potential utility in the clinical diagnosis and treatment of membrane-associated disease.     

Thermodynamics of aqueous carbohydrate surfactant solutions

The paper deals with the application of the micelle formation theory, developed by Nagarajan and Ruckenstein [R. Nagarajan, E. Ruckenstein, Langmuir 7 (1991) 2934–2969] and Nagarajan [R. Nagarajan, in: K. Esumi (Ed.), Structure–Performance Relationships in Surfactants, Dekker, New York, 1997, pp. 1–81; R. Nagarajan, Adv. Colloid Interface Sci. 26 (1986) 205-264] to various n-alkyl-β-d-glucopyranoside surfactants, differing in the surfactant tail length (n-octyl-β-d-glucopyranoside C₈G₁, n-decyl-β-d-glucopyranoside C₁₀G₁ and dodecyl-β-d-glucopyranoside C₁₂G₁). The model predicts that the carbohydrate surfactant molecules assemble for energetic reasons in spherical bilayer vesicles. The critical micellar concentration as function of the temperature shows a minimum value. The formed micellar aggregates exhibit a broad distribution of sizes. It is demonstrated in this study that the thermodynamic theory in combination with phase separation thermodynamics can be used successfully to described the phase separation, which occurs for the system C₁₀G₁+water and C₁₂G₁+water at low surfactant concentrations.     

A Simple Quantitative Method to Study Protein–Lipopolysaccharide Interactions by Using Liquid Crystals

The interaction of proteins with endotoxins has divergent effects on lipopolysaccharide (LPS)‐induced responses, which serve as a basis for many clinical and therapeutic applications. It is, therefore, important to understand these interactions from both theoretical and practical points of view. This paper advances the design of liquid crystal (LC)‐based stimuli‐responsive soft materials for quantitative measurements of LPS–protein binding events through interfacial ordering transition. Micrometer‐thick films of LCs undergo easily visualized ordering transitions in response to proteins at LPS–aqueous interfaces of the LCs. The optical response of the LC changes from dark to bright after aqueous solutions of hemoglobin (Hb), bovine serum albumin (BSA), and lysozyme proteins (LZM) are in contact with a LPS‐laden aqueous–LC interface. The effects of interactions of different proteins with LPS are also observed to cause the response of the LC to vary significantly from one to another; this indicates that manipulation of the protein–LPS binding affinity can provide the basis for a general, facile method to tune the LPS‐induced responses of the LCs to interfacial phenomena. By measuring the optical retardation of the 4′‐pentyl‐4‐cyanobiphenyl (5CB) LC, the binding affinity of the proteins (Hb, BSA, and LZM) towards LPS that leads to different orientational behavior at the aqueous interfaces of the LCs can be determined. The interaction of proteins with the LPS‐laden monolayer is highest for LPS–Hb, followed by LPS–BSA, and least for LPS–LZM; this is in correlation with their increasing order of binding constants (LPS‐Hb>LPS‐BSA>LPS‐LZM). The results presented herein pave the way for quantitative and multiplexed measurements of LPS–protein binding events and reveal the potential of the LC system to be used as quantitative LC‐based, stimuli‐responsive soft materials.     

Novel cationic coating agent for protein separation by capillary electrophoresis†

A novel positively charged surfactant N‐dodecyl‐N,N‐dimethyl‐(1,2‐propandiol) ammonium chloride was used for the dynamic coating of the inner wall of a silica capillary. This paper covers the evaluation of dynamic coating and study of the influence of the analysis conditions for the magnitude and direction of electroosmotic flow as well as for the effective and selective separation of chosen proteins (ribonuclease A, cytochrome c, lysozyme, and myoglobin). The concentration of 0.1 mM of N‐dodecyl‐N,N‐dimethyl‐(1,2‐propandiol) ammonium chloride enabled the reversal of the electro‐osmotic flow, however, to separate basic as well as neutral proteins the higher concentration of the studied surfactant was necessary. The final conditions for the separation of studied proteins were set at 100 mM sodium acetate pH 5.5 with 10.0 mM of the studied surfactant. The results were also compared with those of two commercially available cationic surfactants, cetyltrimethylammonium bromide and dodecyltrimethylammonium bromide. Additionally, the developed method for protein separation was applied for the determination of lysozyme in a cheese sample. The limits of detection and quantification of lysozyme were 0.9 and 3.0 mg/L, respectively. The mean concentration of lysozyme found in the cheese sample was 167.3 ± 10.3 mg/kg.     

Efficiency of blocking of non-specific interaction of different proteins by BSA adsorbed on hydrophobic and hydrophilic surfaces

The efficiency of a pre-absorbed bovine serum albumin (BSA) layer in blocking the non-specific adsorption of different proteins on hydrophobic and hydrophilic surfaces was evaluated qualitatively and quantitatively using infrared reflection spectroscopy supported by spectral simulations. A BSA layer with a surface coverage of 35% of a close-packed monolayer exhibited a blocking efficiency of 90–100% on a hydrophobic and 68–100% on a hydrophilic surface, with respect to the non-specific adsorption of concanavalin A (Con A), immunoglobulin G (IgG), and staphylococcal protein A (SpA). This BSA layer was produced using a solution concentration of 1 mg/mL and 30 min incubation time. BSA layers that were adsorbed at conditions commonly employed for blocking (a 12 h incubation time and a solution concentration of 10 mg/mL) exhibited a blocking activity that involved competitive adsorption–desorption. This activity resulted from the formation of BSA–phosphate surface complexes, which correlated with the conformation of adsorbed BSA molecules that was favourable for blocking. The importance of optimisation of the adsorbed BSA layer for different surfaces and proteins to achieve efficient blocking was addressed in this study.     

Detecting and differentiating Escherichia coli strain TOP10 using optical textures of liquid crystals

We report a method for detecting Escherichia coli using a nematic liquid crystal (LC), 4-cyano-4′-pentylbiphenyl (5CB). Among three E. coli strains tested, TOP10 strain grown on agar plates induces a homeotropic orientation of LCs whereas DH5α and JM109 strains do not. This results in a clear distinction in the optical appearance of LCs as either uniformly dark or bright under polarised light. The LC-based method provides a simple, rapid and low-cost method of identifying E. coli strains.     

Neoverataline A and B, two antifungal alkaloids with a novel carbon skeleton from Veratrum taliense

Bioassay-guided fractionation of the ethanol extract of the roots and rhizomes of Veratrum taliense yielded two new and thirteen known steroidal alkaloids. The structures of the two new compounds, neoverataline A and B, were established by extensive spectroscopic analyses to be 3,4-secocevane-4,9-olid-14,15,16,20-tetra-ol-3-oic acid and 3,4-secocevane-4,9-olid-7,14,15,16,20-penta-ol-3-oic acid, respectively, and are a novel carbon skelton. All of the fifteen alkaloids were subjected to in vitro antifungal assays, which showed that the verazine- (veramitaline, stenophylline B, stenophylline B-3-O-β-d-glucopyranoside, veramiline-3-O-β-d-glucopyranoside) and jerveratrum-type (jervine, jervine-3-O-β-d-glucopyranoside) alkaloids exhibited strong antifungal activities against the phytopathogenic fungus Phytophthora capisis with MICs of 160, 120, 160, 80, 80 and 120 μg·L⁻¹, respectively. Furthermore, the verazine-type alkaloids stenophylline B, stenophylline B 3-O-β-d-glucopyranoside and veramiline 3-O-β-d-glucopyranoside were shown to also inhibit the growth of another fungal phytopathogen Rhizoctonia cerealis with MICs of 160, 120 and 120 μg mL⁻¹. The MICs of triadimefon (an antifungal agrochemical used herein as a positive control) against P. capisis and R. cerealis were 120 and 80 μg mL⁻¹, respectively. A preliminary structure-activity relationship regarding these alkaloids has been formulated.     

Detecting DNA targets through the formation of DNA/CTAB complex and its interactions with liquid crystals

In this paper, we report the formation of a DNA/cetyl trimethylammonium bromide (CTAB) complex on a solid surface and its interaction with a thin layer of liquid crystals (LC) supported on the surface. Our results show that when the surface is decorated with DNA only, the LC gives a bright image, but when the surface is decorated with the DNA/CTAB complex, the LC becomes dark when the surface density of CTAB is above 5.25 ± 0.13 × 10(13)/cm(2). To exploit this phenomenon for detecting DNA targets, we used a surface decorated with electroneutral PNA probes for capturing DNA targets, and then treated the surface with 0.1 mM of CTAB. In the presence of DNA targets, a PNA/DNA/CTAB complex is formed and that leads to a dark image on the thin layer of the LC supported on the surface. Moreover, DNA targets with a complementary, 1-base mismatch and non-complementary sequence can be differentiated by using this method. This study provides a new principle for the label-free detection of DNA targets without any fluorescent labels.     

In silico,in vitro antioxidant and density functional theory based structure activity relationship studies of plant polyphenolics as prominent natural antioxidants

In the present study, different extracts of stem bark of Shorea tumbuggaia and roots of Syzygium alternifolium were screened for total phenolic content (TPC), total flavonoid content (TFC) and in vitro DPPH radical scavenging activity to isolate the natural antioxidants. The bioassay-guided fraction of stem bark of Shorea tumbuggaia yielded three compounds, piceatannol (ST-1), resveratrol-12-C-β-d-glucopyranoside (ST-2) and hopeaphenol (ST-3). Similarly, a systematic phytochemical examination of extracts of Syzygium alternifolium roots had resulted five compounds, 5,7,8,5′-tetramethoxy-3′,4′-methylenedioxyflavone (SA-1), 5-hydroxy-4′,7-dimethoxy-6,8-di-C-methylflavone (SA-2), quercetin 7-methylether (SA-3), kaempferol 7,4′-dimethylether 3-O-β-d-glucopyranoside (SA-4) and taxifolin 3-O-α-l-rhamnopyranoside (SA-5). Structures of the isolates were established using UV, IR, Mass, ¹H and ¹³C NMR spectral studies. Density Functional Theory (DFT) calculations, Molecular docking and Lipinski rule of five were conducted to explored the antioxidant activity of isolated compounds. SA-3 (37.52 µg/mL) and ST-1 (42.43 µg/mL) showed highest IC₅₀ values compared to the Ascorbic acid (45.97 µg/mL) and have highest electron affinities (EA eV) along with smallest HOMO-LUMO energy gap. Molecular docking and binding affinity studies with NADPH and SPSB2 proteins, revealed the prominent antioxidant activity of SA-3 and ST-1 with molecular interaction besides promising solvation energies. Hence, the two compounds maybe useful for the treatment of oxidative damage related diseases.     

Adsorption behaviour and surfactant elution of cationic salivary proteins at solid/liquid interfaces,studied by in situ ellipsometry

Adsorption of the cationic salivary proteins lactoferrin, lactoperoxidase, lysozyme and histatin 5 to pure (hydrophilic) and methylated (hydrophobized) silica surfaces was investigated by in situ ellipsometry. Effects of concentration (≤10 μg ml⁻¹, for lysozyme ≤200 μg ml⁻¹) and dependence of surface wettability, as well as adsorption kinetics and elutability of adsorbed films by buffer and sodium dodecyl sulphate (SDS) solutions were investigated. Results showed that the amounts adsorbed decreased in the order lactoferrin ≥ lactoperoxidase > lysozyme ≥ histatin 5. On hydrophilic silica, the adsorption was most likely driven by electrostatic interactions, which resulted in adsorbed amounts of lactoferrin that indicated the formation of a monolayer with both side-on and end-on adsorbed molecules. For lactoperoxidase the adsorbed amounts were somewhat higher than an end-on monolayer, lysozyme adsorption showed amounts corresponding to a side-on monolayer, and histatin 5 displayed adsorbed amounts in the range of a side-on monolayer. On hydrophobized substrata, the adsorption was also mediated by hydrophobic interactions, which resulted in lower adsorbed amounts of lactoferrin and lactoperoxidase; closer to side-on monolayer coverage. For both lysozyme and histatin 5 the adsorbed amounts were the same as on the hydrophilic silica. The investigated proteins exhibited fast adsorption kinetics, and the initial kinetics indicated mass transport controlled behaviour at low concentrations on both types of substrates. Buffer rinsing and SDS elution indicated that the proteins in general were more tightly bound to the hydrophobized surface compared to hydrophilic silica. Overall, the surface activity of the investigated proteins implicates their importance in the salivary film formation.     

Furostanol saponins with inhibitory action against COX-2 production from Tupistra chinensis rhizomes

Two furostanol saponins were obtained from the n-butanol fraction of methanol extract from Tupistra chinensis rhizomes,a folk medicine of Shennongjia Forest District of Hubei Province.Their structures were determined as (25S)-26-O-(β-D-glucopyranosyl)- furost-1β,3β,22α,26-tetrol-3-O-β-D-glucopyranosyl-(1→4)-β-D-glucopyranosyl-(1→2)-β-D-glucopyranoside (1) and (25R)- 26-O-(β-D-glucopyranosyl)-furost-1β,3β22α,26-tetrol 3-O-β-D-glucopyranosyl-(1→4)-β-D-glucopyranosyl-(1→2)-β-D-glu- copyranoside (2),on basis of chemical and spectroscopic evidences.1 and 2 displayed marked inhibitory action towards COX-2 production in macrophages of the rat abdomen induced by LPS at 20μg/mL.     

Analysis of commercial beverage products by size exclusion chromatography coupled with UV-vis absorbance detection and dynamic surface tension detection

Multidimensional analysis of instant coffee and barley beverage samples using size exclusion chromatography (SEC) combined with a dynamic surface tension detector (DSTD) and a UV-vis absorbance detector (UV) is reported. A unique finding of this study was the action of the tetrabutylammonium (TBA) cation as a modifying agent (with bromide as the counter anion) that substantially increased the surface pressure signal and sensitivity of many of the proteins in the chromatographically separated samples. The tetrabutylammonium bromide (TBAB) enhancement of the surface pressure signal was further investigated by studying the response of 12 commercial standard proteins (α-lactalbumin, β-lactoglobulin, human serum albumin (HSA), albumin from chicken egg white (OVA), bovine serum albumin (BSA), hemoglobin, α-chymotrypsinogen A, cytochrome C, myoglobin, RNase A, carbonic anhydrase, and lysozyme) in buffer performed using flow injection analysis (FIA) coupled with the DSTD with and without various concentrations of TBAB. The FIA-DSTD data show that 1 mM TBAB enhances sensitivity of HSA detection, by lowering the limit of detection (LOD) from 2 mg/mL to 0.1 mg/mL. Similarly, the LOD for BSA was reduced from 1 mg/mL to 0.2 mg/mL. These FIA-DSTD experiments allowed the detection conditions to be optimized for further SEC-UV/DSTD experiments. Thus, the SEC-UV/DSTD system has been optimized and successfully applied to the selective analysis of surface-active protein fractions in a commercial instant coffee sample and in a soluble barley sample. The complementary selectivity of using the DSTD relative to an absorbance detector is also demonstrated.     

Amperometric determination of bonded glucose with an MnO(2) and glucose oxidase bulk-modified screen-printed electrode using flow-injection analysis

A screen-printed amperometric biosensor based on carbon ink double bulk-modified with MnO₂ as a mediator and glucose oxidase as a biocomponent was investigated for its ability to serve as a detector for bonded glucose in different compounds, such as cellobiose, saccharose, (-)-4-nitrophenyl-β-d-glucopyranoside, as well as in beer samples by flow-injection analysis (FIA). The biosensor could be operated under physiological conditions (0.1 M phosphate buffer, pH 7.5) and exhibited good reproducibility and stability. Bonded glucose was released with glucosidase in solution, and the free glucose was detected with the modified screen-printed electrode (SPE). The release of glucose by the aid of glucosidase from cellobiose, saccharose and (-)-4-nitrophenyl-β-d-glucopyranoside in solution showed that stoichiometric quantities of free glucose could be monitored in all three cases.The linear range of the amperometric response of the biosensor in the FIA-mode flow rate 0.2 mL min⁻¹, injection volume 0.25 mL, operation potential 0.48 V versus Ag/AgCl) extends from 11 to 13,900 μmol L⁻¹ glucose in free form. The limit of detection (3σ) is 1 μmol L⁻¹ glucose. A concentration of 100 μmol L⁻¹ yields a relative standard deviation of approximately 7% with five injections. These values correspond to the same concentrations of bonded glucose supposed that it is liberated quantitatively (incubation for 2 h with glucosidase).Bonded glucose could be determined in beer samples using the same assay. The results corresponded very well with the reference procedure.     

Formation of water-soluble vitamin derivatives from lipophilic vitamins by cultured plant cells

Glycosylation of vitamin E, its homologues, and vitamin A by cultured plant cells of Phytolacca americana and Catharanthus roseus was investigated to produce water-soluble vitamin derivatives. Two new compounds, that is, 2,5,7,8-tetramethyl-2-(4-methylpentyl)chroman-6-yl β-d-glucopyranoside and 2,5,7,8-tetramethyl-2-(4,8-dimethylnonyl)chroman-6-yl β-d-glucopyranoside, together with 2,5,7,8-tetramethyl-2-(4,8,12-trimethyltridecyl)chroman-6-yl β-d-glucopyranoside were isolated from the cultured cells of P. americana following administration of vitamin E and its homologues, that is, 2,5,7,8-tetramethyl-2-(4-methylpentyl)-6-chromanol, 2,5,7,8-tetramethyl-2-(4,8-dimethylnonyl)-6-chromanol and 2,5,7,8-tetramethyl-2-(4,8,12-trimethyltridecyl)-6-chromanol (vitamin E). On the other hand, glycosylation by C. roseus gave two new compounds, that is, 2,5,7,8-tetramethyl-2-(4-methylpentyl)chroman-6-yl 6-O-β-d-glucopyranosyl-β-d-glucopyranoside and 2,5,7,8-tetramethyl-2-(4,8-dimethylnonyl)chroman-6-yl 6-O-β-d-glucopyranosyl-β-d-glucopyranoside, as well. Furthermore, conversion of vitamin A (retinol) by these cultured cells afforded retinyl β-d-glucopyranoside.     

Fast cation-exchange separation of proteins in a plastic microcapillary disc

A novel disposable adsorbent material for fast cation-exchange separation of proteins was developed based on plastic microcapillary films (MCFs). A MCF containing 19 parallel microcapillaries, each with a mean internal diameter of 142 μm, was prepared using a melt extrusion process from an ethylene-vinyl alcohol copolymer (EVOH). The MCF was surface functionalised to produce a cation-exchange adsorbent (herein referred as MCF-EVOH-SP). The dynamic binding capacity of the new MCF-EVOH-SP material was experimentally determined by frontal analysis using pure protein solutions in a standard liquid chromatography instrument for a range of superficial flow velocities, u_LS = 5.5–27.7 cm s⁻¹. The mean dynamic binding capacity for hen-egg lysozyme was found to be approximately 100 μg for a 5 m length film, giving a ligand binding density of 413 ng cm⁻². The dynamic binding capacity did not vary significantly over the range of u_LS tested. The application of this novel material to subtractive chromatography was demonstrated for anionic BSA and cationic lysozyme at pH 7.2. The chromatographic separation of two cationic proteins, lysozyme and cytochrome-c, was also performed with a view to applying this technology to the analysis or purification of proteins. Future applications might include separation based on anion exchange and other modes of adsorption.     

Circular dichroism and fluorescence spectroscopy studies of the effect of cyclodextrins on the thermal stability of chicken egg white lysozyme in aqueous solution

Circular dichroism spectroscopy revealed that the thermal stability of chicken egg white lysozyme in an aqueous buffer solution is significantly lowered by the addition of 6-O-α-d-glucosyl-β-cyclodextrin (G1-β-CD), whereas it is raised by the addition of methyl α-d-glucopyranoside. The α- and γ-cyclodextrin also lowered the thermal stability, although the effects were less prominent than that of G1-β-CD. Fluorescence spectroscopy suggested that cyclodextrins include the side chains of tryptophan residues within their internal cavities to lower the thermal stability of lysozyme. The fluorescence intensity of a sample, re-cooled to 25 °C after thermal denaturation at 75 °C in the presence of G1-β-CD, was stronger than that observed for native lysozyme. The fact that the fluorescence intensity of the re-cooling sample was stronger than that of the native one indicates that G1-β-CD persists in binding to the side chains of tryptophan residues of the re-cooled lysozyme.     

Protein triggered ordering transitions in poly (L-lysine)-coated liquid crystal emulsion droplets

Here, we report a simple and label-free methodology for real-time monitoring of adsorption of proteins such as bovine serum albumin (BSA), concanavalin A (ConA) (a lectin) and cathepsin D (CathD) (a tumour marker) on micrometer-sized poly (L-lysine) (PLL) functionalised liquid crystal (LC) droplets dispersed in aqueous phases. Earlier, we had demonstrated that PLL, a positively charged natural peptide, can induce homeotropic ordering of LCs at LC-aqueous interface, and thus PLL-adsorbed LC droplets showed radial director configuration. Herein, it was observed that subsequent non-specific adsorption of anionic proteins such as BSA, ConA and CathD can trigger a quick transition in director configuration of PLL-LC droplets (primarily dominated by electrostatic interactions) to pre-radial or bipolar, thus acting as a simple optical probe for detection of these proteins up to μg/mL of concentrations. Further, the detection limits for these proteins are found to vary (BSA<ConA<CathD) which follow the similar order as their anionic charges, thus suggesting the role of different binding affinities of protein-PLL in realising the director configuration of LC droplets. Overall, this study offers new pathways utilising ordering transition in LC droplets which will strengthen the principles to recognise biomolecular interactions for various interfacial and sensing applications.     

Glass substrates crosslinked with tetracycline-imprinted polymeric silicate and CdTe quantum dots as fluorescent sensors

A fluorescence-based sensor that combines the merits of quantum dots (QDs) and molecularly imprinted polymers (MIPs) was first fabricated on a glass substrate via a sol–gel route. Some of the key performance factors, including silane selection, substrate etching, the reaction times of glass silanization and sol–gel polymerization, and the times and methods used for template stripping and loading, were discussed and determined. After fabricating the sensor on either a 3-aminopropyltriethoxysilane (APS) or a 3-mercaptopropyltriethoxysilane (MPS) modified glass substrate, APS showed a much better performance than MPS as both the capping reagent of QDs and the functional monomer of tetracycline-templated MIPs. The APS-QDs on APS-modified glass had a higher imprinted factor (IF = 5.6), a lower LOD (2.1 μM, 3σ), and a more stable signal (2.8%, n = 10 at 70 μM) than those on the MPS-modified glass (IF = 5.2, LOD = 6.5 μM, stability = 6.2%). Furthermore, the recoveries of tetracycline (70 μM) from BSA (133 μg/mL) and FBS (0.66 ppt) by the APS-modified glass were 98% (RSD = 3.5%, n = 5) and 97% (RSD = 5.7%), respectively. For the MPS-modified glass, recoveries of 95% (RSD = 7.2%) and 89% (RSD = 8.7%) were observed at 67 μg/mL of BSA and 0.33 ppt of FBS, respectively.     

Rapid detection of pathogenic bacteria based on a universal dual-recognition FRET sensing system constructed with aptamer-quantum dots and lectin-gold nanoparticles

The threat to public health from bacterial infections has led to an urgent need to develop simpler, faster and more reliable bacterial detection methods. In this work, we developed a universal dual-recognition based sandwich fluorescence resonance energy transfer (FRET) sensor by using specific aptamer-modified quantum dots (Aptamer-QDs) as energy donor and lectin concanavalin A (Con A) modified gold nanoparticles (Con A-AuNPs) as energy acceptor to achieve rapid and sensitive detection of Escherichia coli (E. coli) within 0.5 h. In the presence of the target E. coli, the energy donor of Aptamer-QDs and acceptor of Con A-AuNPs were close to each other, causing changes of FRET signals. Based on the constructed FRET sensor, a linear detection range of from 10² cfu/mL to 2 × 10⁸ cfu/mL with the detection limit of 45 cfu/mL for E. coli was achieved. Furthermore, the FRET sensor was applied to detect E. coli in the milk and orange juice with the detection limit of 300 cfu/mL and 200 cfu/mL, respectively and recovery rate from 83.1% to 112.5%. The strategy holds great promise in pathogenic bacteria detection due to its rapid and sensitivity.