A Novel Label-Free Optical Biosensor Using Synthetic Oligonucleotides from E. coli O157:H7: Elementary Sensitivity Tests

Interdigitated Electrode Biosensor Based on Plasma-Deposited TiO2 Nanoparticles for Detecting DNA

Bioelectrodes mediated by metal oxide nanoparticles have facilitated the development of new sensors in medical diagnosis. High-purity TiO₂ nanoparticles (NPs) were synthesized through thermal plasma and deposited directly on an interdigitated electrode. The surface of the TiO₂-deposited electrode was activated with (3-aminopropyl) triethoxysilane (APTES) followed by fixing the single-stranded probe deoxyribonucleic acid (DNA) to fabricate the DNA biosensor. The structural properties of the deposited TiO₂ nanoparticles were analyzed using a transmission electron microscope (TEM), X-ray diffraction (XRD), and a dynamic light scattering (DLS) system. The chemical composition and structural properties of the TiO₂ nanoparticle layer and the fixed layer were analyzed by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). E. coli O157:H7, a well-known pernicious pathogenic bacterial species, was detected as a target DNA of the prepared DNA biosensor, and the characteristics of DNA detection were determined by the current change using a picoammeter. The degree of binding between the probe DNA and the target DNA was converted into an electrical signal using the picoammeter method to quantitatively analyze the concentration of the target DNA. With the specificity experiment, it was confirmed that the biosensor was able to discriminate between nucleotides with mismatched, non-complementary, or complementary sequences.

Label-Free Detection of E. coli O157:H7 DNA Using Light-Addressable Potentiometric Sensors with Highly Oriented ZnO Nanorod Arrays

The detection of bacterial deoxyribonucleic acid (DNA) is of great significance in the quality control of food and water. In this study, a light-addressable potentiometric sensor (LAPS) deposited with highly oriented ZnO nanorod arrays (NRAs) was used for the label-free detection of single-stranded bacterial DNA (ssDNA). A functional, sensitive surface for the detection of Escherichia coli (E. coli) O157:H7 DNA was prepared by the covalent immobilization of the specific probe single-stranded DNA (ssDNA) on the LAPS surface. The functional surface was exposed to solutions containing the target E. coli ssDNA molecules, which allowed for the hybridization of the target ssDNA with the probe ssDNA. The surface charge changes induced by the hybridization of the probe ssDNA with the target E. coli ssDNA were monitored using LAPS measurements in a label-free manner. The results indicate that distinct signal changes can be registered and recorded to detect the target E. coli ssDNA. The lower detection limit of the target ssDNA corresponded to 1.0 × 102 colony forming units (CFUs)/mL of E. coli O157:H7 cells. All the results demonstrate that this DNA biosensor, based on the electrostatic detection of ssDNA, provides a novel approach for the sensitive and effective detection of bacterial DNA, which has promising prospects and potential applications in the quality control of food and water.

Label-free real-time optical monitoring of DNA hybridization using SiN Mach-Zehnder interferometer-based integrated biosensing platform

We report on the label-free real-time optical monitoring of DNA hybridization upon exposure to a flow of complementary DNA at different concentrations. The biosensor is composed of a silicon nitride integrated unbalanced Mach-Zehnder interferometer (MZI), with an integrated arrayed waveguide grating as a spectral filter. This MZI has been shown to have both sufficient multiplexing capability and limit of detection on the order of 10  -  6 RIU. Probe DNA, consisting of a 36-mer fragment is covalently immobilized on the silicon nitride integrated biosensor. The wavelength shift is monitored upon complementary DNA targets being flown over the sensor. Concentrations of 1 pM can be easily detected. Also, an alternative route to modify the sensor surface with carboxylic groups using the photochemical reaction of fatty acids is proposed and preliminary XPS results are presented. Moreover, preliminary results for DNA obtained from a rolling circle amplification (RCA-DNA) process and spiked in a realistic amplification buffer are presented.

Sensitive Leptospira DNA detection using tapered optical fiber sensor

This paper presents the development of tapered optical fiber sensor to detect a specific Leptospira bacteria DNA. The bacteria causes Leptospirosis, a deadly disease but with common early flu-like symptoms. Optical single mode fiber (SMF) of 125 μm diameter is tapered to produce 12 μm waist diameter and 15 cm length. The novel DNA-based optical fiber sensor is functionalized by incubating the tapered region with sodium hydroxide (NaOH), (3-Aminopropyl) triethoxysilane and glutaraldehyde. Probe DNA is immobilized onto the tapered region and subsequently hybridized by its complementary DNA (cDNA). The transmission spectra of the DNA-based optical fiber sensor are measured in the 1500 to 1600 nm wavelength range. It is discovered that the shift of the wavelength in the SMF sensor is linearly proportional with the increase in the cDNA concentrations from 0.1 to 1.0 nM. The sensitivity of the sensor toward DNA is measured to be 1.2862 nm/nM and able to detect as low as 0.1 fM. The sensor indicates high specificity when only minimal shift is detected for non-cDNA testing. The developed sensor is able to distinguish between actual DNA of Leptospira serovars (Canicola and Copenhageni) against Clostridium difficile (control sample) at very low (femtomolar) target concentrations.

Lysozyme aptasensor based on a glassy carbon electrode modified with a nanocomposite consisting of multi-walled carbon nanotubes, poly(diallyl dimethyl ammonium chloride) and carbon quantum dots

An aptamer-based method is described for electrochemical determination of lysozyme. A glassy carbon electrode was modified with a nanocomposite composed of multi-walled carbon nanotubes, poly(diallyl dimethyl ammonium chloride), and carbon quantum dots. The composition of the nanocomposite (MWCNT/PDDA/CQD) warrants good electrical conductivity and a high surface-to-volume ratio. The lysozyme-binding aptamers were immobilized on the nanocomposite via covalent coupling between the amino groups of the aptamer and the carboxy groups of the nanocomposite. The modified electrode was characterized by electrochemical impedance spectroscopy, cyclic voltammetry and differential pulse voltammetry. The use of this nanocomposite results in a considerable enhancement of the electrochemical signal and contributes to improving sensitivity. Hexacyanoferrate was used as an electrochemical probe to study the dependence of the peak current on lysozyme concentration. In the presence of lysozyme, the interaction of lysozyme with immobilized aptamer results in a decrease of the peak current, best measured at +0.15 V vs. Ag/AgCl. A plot of peak current changes versus the logarithm of the lysozyme concentration is linear in the 50 fmol L^-1 to 10 nmol L^-1 concentration range, with a 12.9 fmol L^-1 detection limit (at an S/N ratio of 3). The method is highly reproducible, specific and sensitive, and the electrode has a rapid response. It was applied to the determination of lysozyme in egg white, serum, and urine. Graphical abstract Schematic of a nanocomposite composed of multi-walled carbon nanotubes (MWCNTs), poly(diallyldimethyl ammonium chloride) (PDDA), and carbon quantum dots (CQDs) for use in a lysozyme aptasensor. The aptamer was immobilized on the surface, and bovine serum albumin (BSA) was applied to block the surface. The changes of peak current for the electrochemical probe hexacyanoferrate (Fe(CN)₆^3-/4-) in the presence and absence of lysozyme was traced.

An electrochemical aptasensor based on TiO2/MWCNT and a novel synthesized Schiff base nanocomposite for the ultrasensitive detection of thrombin

A sensitive aptasensor based on a robust nanocomposite of titanium dioxide nanoparticles, multiwalled carbon nanotubes (MWCNT), chitosan and a novel synthesized Schiff base (SB) (TiO2/MWCNT/CHIT/SB) on the surface of a glassy carbon electrode (GCE) was developed for thrombin detection. The resultant nanocomposite can provide a large surface area, excellent electrocatalytic activity, and high stability, which would improve immobilization sites for biological molecules, allow remarkable amplification of the electrochemical signal and contribute to improved sensitivity. Thrombin aptamers were simply immobilized onto the TiO2-MWCNT/CHIT-SB nanocomposite matrix through simple π - π stacking and electrostatic interactions between CHIT/SB and aptamer strands. The electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were used to analyze the surface characterization of unmodified GCE and TiO2-MWCNT/CHIT-SB modified GCE, and also the interaction between aptamer and thrombin. In the presence of thrombin, the aptamer on the adsorbent layer captures the target on the electrode interface, which makes a barrier for electrons and inhibits electron transfer, thereby resulting in decreased DPV and increased impedance signals of the TiO2-MWCNT/CHIT-SB modified GCE. Furthermore, the proposed aptasensor has a very low LOD of 1.0fmolL(-1) thrombin within the detection range of 0.00005-10nmolL(-1). The aptasensor also presents high specificity and reproducibility for thrombin, which is unaffected by the coexistence of other proteins. Clinical application was performed with analysis of the thrombin levels in blood and CSF samples obtained from patients with MS, Parkinson, Epilepsy and Polyneuropathy using both the aptasensor and commercial ELISA kit. The results revealed the proposed system to be a promising candidate for clinical analysis of thrombin.

Titanium Dioxide Nanoparticle-Based Interdigitated Electrodes: A Novel Current to Voltage DNA Biosensor Recognizes E. coli O157:H7

Nanoparticle-mediated bio-sensing promoted the development of novel sensors in the front of medical diagnosis. In the present study, we have generated and examined the potential of titanium dioxide (TiO₂) crystalline nanoparticles with aluminium interdigitated electrode biosensor to specifically detect single-stranded E.coli O157:H7 DNA. The performance of this novel DNA biosensor was measured the electrical current response using a picoammeter. The sensor surface was chemically functionalized with (3-aminopropyl) triethoxysilane (APTES) to provide contact between the organic and inorganic surfaces of a single-stranded DNA probe and TiO₂ nanoparticles while maintaining the sensing system’s physical characteristics. The complement of the target DNA of E. coli O157:H7 to the carboxylate-probe DNA could be translated into electrical signals and confirmed by the increased conductivity in the current-to-voltage curves. The specificity experiments indicate that the biosensor can discriminate between the complementary sequences from the base-mismatched and the non-complementary sequences. After duplex formation, the complementary target sequence can be quantified over a wide range with a detection limit of 1.0 x 10^-13M. With target DNA from the lysed E. coli O157:H7, we could attain similar sensitivity. Stability of DNA immobilized surface was calculated with the relative standard deviation (4.6%), displayed the retaining with 99% of its original response current until 6 months. This high-performance interdigitated DNA biosensor with high sensitivity, stability and non-fouling on a novel sensing platform is suitable for a wide range of biomolecular interactive analyses.

Amorphous silicon p-i-n structure acting as light and temperature sensor

In this work, we propose a multi-parametric sensor able to measure both temperature and radiation intensity, suitable to increase the level of integration and miniaturization in Lab-on-Chip applications. The device is based on amorphous silicon p-doped/intrinsic/n-doped thin film junction. The device is first characterized as radiation and temperature sensor independently. We found a maximum value of responsivity equal to 350 mA/W at 510 nm and temperature sensitivity equal to 3.2 mV/K. We then investigated the effects of the temperature variation on light intensity measurement and of the light intensity variation on the accuracy of the temperature measurement. We found that the temperature variation induces an error lower than 0.55 pW/K in the light intensity measurement at 550 nm when the diode is biased in short circuit condition, while an error below 1 K/µW results in the temperature measurement when a forward bias current higher than 25 µA/cm² is applied.

Biomimetic receptors for bioanalyte detection by quartz crystal microbalances - from molecules to cells

A universal label-free detection of bioanalytes can be performed with biomimetic quartz crystal microbalance (QCM) coatings prepared by imprinting strategies. Bulk imprinting was used to detect the endocrine disrupting chemicals (EDCs) known as estradiols. The estrogen 17β-estradiol is one of the most potent EDCs, even at very low concentrations. A highly sensitive, selective and robust QCM sensor was fabricated for real time monitoring of 17β-estradiol in water samples by using molecular imprinted polyurethane. Optimization of porogen (pyrene) and cross-linker (phloroglucinol) levels leads to improved sensitivity, selectivity and response time of the estradiol sensor. Surface imprinting of polyurethane as sensor coating also allowed us to generate interaction sites for the selective recognition of bacteria, even in a very complex mixture of interfering compounds, while they were growing from their spores in nutrient solution. A double molecular imprinting approach was followed to transfer the geometrical features of natural bacteria onto the synthetic polymer to generate biomimetic bacteria. The use of biomimetic bacteria as template makes it possible to prepare multiple sensor coatings with similar sensitivity and selectivity. Thus, cell typing, e.g., differentiation of bacteria strains, bacteria growth profile and extent of their nutrition, can be monitored by biomimetic mass sensors. Obviously, this leads to controlled cell growth in bioreactors.

Aptasensor and genosensor methods for detection of microbes in real world samples

The increasing concerns about food and environmental safety have prompted the desire to develop rapid, specific, robust and highly sensitive methods for the detection of microorganisms to ensure public health. Although traditional microbiological methods are available, they are labor intensive, unsuitable for on-site and high throughput analysis, and need well-trained personnel. To circumvent these drawbacks, many efforts have been devoted towards the development of biosensors, using nucleic acid as bio-recognition element. In this review, we will focus on recent significant advances made in two types of DNA-based biosensors, namely genosensors, and aptasensors. In genosensor approach, DNA or RNA target is detected through the hybridization reaction between DNA or RNA and ssDNA sensing element, while in aptasensor method, DNA or RNA aptamer, capable of binding to a target molecule with high affinity and specificity, plays the role of receptor. The goal of this article is to review the innovative methods that have been emerged in genosensor and aptasensor during recent years. Particular attention is given to recent advances and trends in selection of biorecognition element, DNA immobilization strategies and sensing formats.

Ultrasonic-assisted self-assembly of monolayer graphene oxide for rapid detection of Escherichia coli bacteria

Due to potential risks to the environment and human health arising from pathogens/chemical contaminants, novel devices are being developed for rapid and precise detection of those contaminants. Here, we demonstrate highly sensitive and selective field-effect transistor (FET) sensor devices for detection of Escherichia coli (E. coli) bacteria using thermally reduced monolayer graphene oxide (TRMGO) sheets as semiconducting channels. The graphene oxide (GO) sheets are assembled on the aminoethanethiol (AET)-functionalized gold (Au) electrodes through electrostatic interactions with ultrasonic assistance. Anti-Escherichia coli (anti-E. coli) antibodies are used as receptors for selective detection of E. coli cells and integrated on the FET device through covalent bonding with Au nanoparticles on the GO surface. The TRMGO FET device shows great electronic stability and high sensitivity to E. coli cells with a concentration as low as 10 colony-forming units (cfu) per mL. The biosensing platform reported here is promising for large-scale, sensitive, selective, low-cost, and real-time detection of E. coli bacteria.

Colorimetric and electrochemical genosensors for the detection of Escherichia coli DNA without amplification in seawater

Monitoring seawater, particularly recreational water, for indicator bacteria presence is required to protect the public from exposure to fecal pollution and to guarantee the safety of the swimming areas. Two methods for the detection and quantification of Escherichia coli DNA were developed: a colorimetric assay in a microplate and an electrochemical biosensor. These assays were based on the double hybridization recognition of a single-strand DNA capture probe immobilized onto the microplate or the screen-printed carbon electrode to its complementary ssDNA, which is hybridized with an ssDNA signal probe labeled with horseradish peroxidase enzyme. The hybridization recognition step used the colorimetric monitoring of the oxidation state of the 3,3',5,5'-tetramethylbenzidine. The electrochemical monitoring of the oxidation state of 5 methyl-phenazinium methyl sulfate was allowed when the horseradish-peroxidase was in the presence of the mediator (5 methyl-phenazinium methyl sulfate and hydrogen peroxide). These approaches allow for the detection and quantification of 10(2) to 10(3) cells of E. coli in 5l of seawater samples in less than 5h. Detection was achieved without a nucleic acid amplification step. The specificity of the two methods against E. coli was demonstrated by testing a panel of bacteria. The two methods can be used for on-site monitoring of seawater quality.

Chemical surface modifications for the development of silicon-based label-free integrated optical (IO) biosensors: a review

Increasing interest has been paid to label-free biosensors in recent years. Among them, refractive index (RI) optical biosensors enable high density and the chip-scale integration of optical components. This makes them more appealing to help develop lab-on-a-chip devices. Today, many RI integrated optical (IO) devices are made using silicon-based materials. A key issue in their development is the biofunctionalization of sensing surfaces because they provide a specific, sensitive response to the analyte of interest. This review critically discusses the biofunctionalization procedures, assay formats and characterization techniques employed in setting up IO biosensors. In addition, it provides the most relevant results obtained from using these devices for real sample biosensing. Finally, an overview of the most promising future developments in the fields of chemical surface modification and capture agent attachment for IO biosensors follows.