Au Nanoparticle Conjugation for Impedance and Capacitance Signal Amplification in Biosensors

Multiplexed Signal Ion Emission Reactive Release Amplification (SIERRA) Assay for the Culture-Free Detection of Gram-Negative and Gram-Positive Bacteria and Antimicrobial Resistance Genes

The global prevalence of antibiotic-resistant bacteria has increased the risk of dangerous infections, requiring rapid diagnosis and treatment. The standard method for diagnosis of bacterial infections remains dependent on slow culture-based methods, carried out in central laboratories, not easily extensible to rapid identification of organisms, and thus not optimal for timely treatments at the point-of-care (POC). Here, we demonstrate rapid detection of bacteria by combining electrochemical immunoassays (EC-IA) for pathogen identification with confirmatory quantitative mass spectral immunoassays (MS-IA) based on signal ion emission reactive release amplification (SIERRA) nanoparticles with unique mass labels. This diagnostic method uses compatible reagents for all involved assays and standard fluidics for automatic sample preparation at POC. EC-IA, based on alkaline phosphatase-conjugated pathogen-specific antibodies, quantified down to 104 bacteria per sample when testing Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa lysates. EC-IA quantitation was also obtained for wound samples. The MS-IA using nanoparticles against S. aureus, E. coli, Klebsiella pneumoniae, and P. aeruginosa allowed selective quantitation of ∼105 bacteria per sample. This method preserves bacterial cells allowing extraction and amplification of 16S ribosomal RNA genes and antibiotic resistance genes, as was demonstrated through identification and quantitation of two strains of E. coli, resistant and nonresistant due to β-lactamase cefotaximase genes. Finally, the combined immunoassays were compared against culture using remnant deidentified patient urine samples. The sensitivities for these immunoassays were 83, 95, and 92% for the prediction of S. aureus, P. aeruginosa, and E. coli or K. pneumoniae positive culture, respectively, while specificities were 85, 92, and 97%. The diagnostic platform presented here with fluidics and combined immunoassays allows for pathogen isolation within 5 min and identification in as little as 15 min to 1 h, to help guide the decision for additional testing, optimally only on positive samples, such as multiplexed or resistance gene assays (6 h).

Ultrasensitive interdigitated capacitance immunosensor using gold nanoparticles

Immunosensors based on interdigitated electrodes (IDEs), have recently demonstrated significant improvements in the sensitivity of capacitance detection. Herein, a novel type of highly sensitive, compact and portable immunosensor based on a gold interdigital capacitor has been designed and developed for the rapid detection of hepatitis B surface antigen (HBsAg). To improve the efficiency of antibody immobilization and time-saving, a self-assembled monolayer (SAM) of 2-mercaptoethylamine film was coated on IDEs. Afterwards, carboxyl groups on primary antibodies were activated through 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and were immobilized on amino-terminated SAM for better control of the oriented immobilization of antibodies on gold IDEs. In addition, gold nanoparticles conjugated with a secondary antibody were used to enhance the sensitivity. Under optimal conditions, the immunosensor exhibited the sensitivity of 0.22 nF.pg ml^-1, the linear range from 5 pg ml^-1 to 1 ng ml^-1 and the detection limit of 1.34 pg ml^-1, at a signal-to-noise ratio of 3.

In situ crystal growth of gold nanocrystals on upconversion nanoparticles for synergistic chemo-photothermal therapy

A multifunctional cancer therapy nanocomposite was proposed and synthesized by linking the pH-responsive SH-PEG-DOX prodrug onto gold nanocrystals that were grown in situ on the surface of upconversion nanoparticles (UCNPs). In the structure of the SH-PEG-DOX prodrug, a hydrazone bond was utilized for subsequent pH-responsive drug release in the intracellular acidic microenvironment of cancer cells. This innovative assembly method is facile and mild, and can be used to obtain nanocomposites of UCNPs and gold, which show excellent photostability and biocompatibility. The final UCNPs@Au-DOX nanocomposites offer efficient treatment effects in vitro under irradiation with an 808 nm laser due to the synergistic effect of chemotherapy and photothermal therapy. In addition, the UCNPs@Au-DOX nanocomposites show excellent intracellular locating ability via upconversion luminescence (UCL) imaging with Er³⁺ ions and magnetic resonance imaging (MRI) with Gd³⁺ ions, indicating that they have potential as a visual tracking agent in cancer treatment. Therefore, the presented bioimaging-guided multifunctional synergistic therapy nanocomposites are promising tools for imaging-guided cancer therapy.

Acetylcholinesterase biosensor for carbaryl detection based on interdigitated array microelectrodes

In this study, an acetylcholinesterase (AChE) biosensor with superior accuracy and sensitivity was successfully developed based on interdigitated array microelectrodes (IAMs). IAMs have a series of parallel microband electrodes with alternating microbands connected together. Chitosan was used as the enzyme immobilization material, and AChE was used as the model enzyme for carbaryl detection to fabricate AChE biosensor. Electrochemical impedance spectroscopy was used in conjunction with the fabricated biosensor to detect pesticide residues. Based on the inhibition of pesticides on the AChE activity, using carbaryl as model compounds, the biosensor exhibited a wide range, low detection limit, and high stability. Moreover, the biosensor can also be used as a new promising tool for pesticide residue analysis.

A regenerating self-assembled gold nanoparticle-containing electrochemical impedance sensor

We report on the development of an electrochemical reductive desorption protocol for repeated regeneration of gold electrodes modified with multi-layers of self-assembled surfaces for use in electrochemical sensing. The gold electrodes were first modified with 1,6-hexanedithiol to which gold nanoparticles were attached in a subsequent modification step. Attachment of thiolated single-stranded nucleic acid oligomers to the gold nanoparticles completed the electrochemical sensor. The changes of electrode behavior after each assembly and desorption processes were investigated by cyclic voltammetry, electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy techniques. The self-assembled sensor showed a wide dynamic range (0.1-100 nM), a low detection limit (20 pM) and high reproducibility (4.4% RSD) for complementary nucleic acid target molecules, along with reusability. On a single gold electrode, the complete sensor-target structure could be assembled and disassembled at least four times with 90% of its original signal intact.

Iron deposition following chronic myocardial infarction as a substrate for cardiac electrical anomalies: initial findings in a canine model

Purpose

Iron deposition has been shown to occur following myocardial infarction (MI). We investigated whether such focal iron deposition within chronic MI lead to electrical anomalies.

Methods

Two groups of dogs (ex-vivo (n = 12) and in-vivo (n = 10)) were studied at 16 weeks post MI. Hearts of animals from ex-vivo group were explanted and sectioned into infarcted and non-infarcted segments. Impedance spectroscopy was used to derive electrical permittivity () and conductivity (). Mass spectrometry was used to classify and characterize tissue sections with (IRON+) and without (IRON-) iron. Animals from in-vivo group underwent cardiac magnetic resonance imaging (CMR) for estimation of scar volume (late-gadolinium enhancement, LGE) and iron deposition (T2*) relative to left-ventricular volume. 24-hour electrocardiogram recordings were obtained and used to examine Heart Rate (HR), QT interval (QT), QT corrected for HR (QTc) and QTc dispersion (QTcd). In a fraction of these animals (n = 5), ultra-high resolution electroanatomical mapping (EAM) was performed, co-registered with LGE and T2* CMR and were used to characterize the spatial locations of isolated late potentials (ILPs).

Results

Compared to IRON- sections, IRON+ sections had higher, but no difference in. A linear relationship was found between iron content and (p<0.001), but not (p = 0.34). Among two groups of animals (Iron (<1.5%) and Iron (>1.5%)) with similar scar volumes (7.28%±1.02% (Iron (<1.5%)) vs 8.35%±2.98% (Iron (>1.5%)), p = 0.51) but markedly different iron volumes (1.12%±0.64% (Iron (<1.5%)) vs 2.47%±0.64% (Iron (>1.5%)), p = 0.02), QT and QTc were elevated and QTcd was decreased in the group with the higher iron volume during the day, night and 24-hour period (p<0.05). EAMs co-registered with CMR images showed a greater tendency for ILPs to emerge from scar regions with iron versus without iron.

Conclusion

The electrical behavior of infarcted hearts with iron appears to be different from those without iron. Iron within infarcted zones may evolve as an arrhythmogenic substrate in the post MI period.

Electrochemical impedance spectroscopic sensing of methamphetamine by a specific aptamer

INTRODUCTION

Electrochemical impedance spectroscopy (EIS) is a simple and highly sensitive technique that can be used for evaluation of the aptamer-target interaction even in a label-free approach.

METHODS

To pursue the effectiveness of EIS, in the current study, the folding properties of specific aptamer for methamphetamine (METH) (i.e., aptaMETH) were evaluated in the presence of METH and amphetamine (Amph). Folded and unfolded aptaMETH was mounted on the gold electrode surface and the electron charge transfer was measured by EIS.

RESULTS

The Ret of methamphetamine-aptaMETH was significantly increased in comparison with other folding conditions, indicating specific detection of METH by aptaMETH.

CONCLUSION

Based on these findings, methamphetamine-aptaMETH on the gold electrode surface displayed the most interfacial electrode resistance and thus the most folding situation. This clearly indicates that the aptaMETH can profoundly and specifically pinpoint METH; as a result we suggest utilization of this methodology for fast and cost-effective identification of METH.

Real-time detection of β1 integrin expression on MG-63 cells using electrochemical impedance spectroscopy

Beta 1 integrin is a membrane protein responsible for attachment and migration of osteosarcoma cells. In this study, expression of β1 integrin on MG-63 cells, a human osteogenic sarcoma cell line, was monitored using electrochemical impedance spectroscopy (EIS). ITO-based biochips were developed using a semiconductor technique. Differences in electric resistance (ΔR) were measured continuously when cells binding with anti-β1 integrin antibody coagulated with nano-scale gold particles. The results of the EIS system were compared with traditional immunofluorescence staining. We found that sample chambers with higher cell densities had larger ΔR values. When the cell densities increased from 5 × 10(4) cells/ml to 5 × 10(5) cells/ml, the ΔR value dose-dependently increased from 14 Ω to 37 Ω. In addition, a highly linear relationship (correlation coefficient, 0.921) was found between the ΔR values and the corresponding fluorescence intensities (p<0.05). These results suggest that electrochemical impedance spectroscopy can be a useful tool for evaluating β1 integrin expression on cell membranes.

Evaluation study of a portable impedance biosensor for detection of avian influenza virus

Current methods for detection of avian influenza virus (AIV) based on virus culture and RT-PCR are well established, but they are either time consuming or require specialized laboratory facilities and highly trained technicians. A simple, rapid, robust, and reliable test, suitable for use in the field or at the patient's bedside, is urgently needed. In this study, the performance of a newly developed portable impedance biosensor was evaluated by comparison with real-time reverse transcriptase PCR (rRT-PCR) and virus culture for detection of AIV in tracheal and cloacal swab samples collected from experimentally H5N2 AIV infected chickens. The impedance biosensor system was based on a combination of magnetic nanobeads, which were coated with AIV subtype-specific antibody for capture (separation and concentration) of a target virus, and a microfluidic chip with an interdigitated array microelectrode for transfer and detection of target virus, and impedance measurement of the bio-nanobeads and AI virus complexes in a buffer solution. A comparison of results obtained from 59 swab samples using virus culture, impedance biosensor and rRT-PCR methods showed that the impedance biosensor technique was comparable in sensitivity and specificity to rRT-PCR. Detection time for the impedance biosensor is less than 1h.

Electrochemical impedance spectroscopy

This review describes recent advances in electrochemical impedance spectroscopy (EIS) with an emphasis on its novel applications to various electrochemistry-related problems. Section 1 discusses the development of new EIS techniques to reduce measurement time. For this purpose, various forms of multisine EIS techniques were first developed via a noise signal synthesized by mixing ac waves of various frequencies, followed by fast Fourier transform of the signal and the resulting current. Subsequently, an entirely new concept was introduced in which true white noise was used as an excitation source, followed by Fourier transform of both excitation and response signals. Section 2 describes novel applications of the newly developed techniques to time-resolved impedance measurements as well as to impedance imaging. Section 3 is devoted to recent applications of EIS techniques, specifically traditional measurements in various fields with a special emphasis on biosensor detections.

Electrical detection of oligonucleotide using an aggregate of gold nanoparticles as a conductive tag

Sequence-specific DNA detection is a routine job in medical diagnostics and genetic screening. Alternative to a fluorescence readout scheme or electrophoresis approach, various kinds of rapid, low-cost, facile, and label-free methods have also been developed in last decades. Among these, direct electrical detection of DNA received increasing attention but more research is desirable. Particularly, enhancement with high discrimination must be employed to selectively amplify the responding signal. A chip-based biosensor was developed in this work to electrically detect 22-mer oligonucleotide DNA at low concentration, from 50 fM to 10 pM. First, a gold nanoparticle (NP) was capped with 3-mercaptopropionic acid through a thiol-gold bond. The derivatized carboxylic acid group showed strong complex interaction with an inorganic linker, Zr(4+). As a result, Zr(4+) could link several hundreds of individual gold NPs together to form an aggregate of nanoparticles (ANP), which was capable of being used as a conductive tag for the electrical detection of DNA. Second, in order to achieve the discriminative localization of ANP to bridge two comb-shaped electrodes (with height of approximately 50 nm and interdistance of 300-350 nm) gapped with insulative material of silicon oxide, peptide nucleic acids were covalently bonded to the silicon oxide in the gap as capture sites for DNA. After hybridization with target DNA, the charged phosphate-containing backbone of DNA was introduced into the gap. Phosphate groups also exhibited strong complex interaction with the linker of Zr(4+) and could react with the residual Zr(4+) on the ANP surface. As a consequence, the conductive tags were linked to the phosphate groups and localized into the gap, which could modify the conductance between the two comb-shaped electrodes in turn. The degree of modification correlated directly to the amount of hybridized DNA and to the concentration of target DNA in sample solution. Compared with the individual NPs used as the tag, a strong enhancement from the gold ANP was obtained.

Recent development of nano-materials used in DNA biosensors

As knowledge of the structure and function of nucleic acid molecules has increased, sequence-specific DNA detection has gained increased importance. DNA biosensors based on nucleic acid hybridization have been actively developed because of their specificity, speed, portability, and low cost. Recently, there has been considerable interest in using nano-materials for DNA biosensors. Because of their high surface-to-volume ratios and excellent biological compatibilities, nano-materials could be used to increase the amount of DNA immobilization; moreover, DNA bound to nano-materials can maintain its biological activity. Alternatively, signal amplification by labeling a targeted analyte with nano-materials has also been reported for DNA biosensors in many papers. This review summarizes the applications of various nano-materials for DNA biosensors during past five years. We found that nano-materials of small sizes were advantageous as substrates for DNA attachment or as labels for signal amplification; and use of two or more types of nano-materials in the biosensors could improve their overall quality and to overcome the deficiencies of the individual nano-components. Most current DNA biosensors require the use of polymerase chain reaction (PCR) in their protocols. However, further development of nano-materials with smaller size and/or with improved biological and chemical properties would substantially enhance the accuracy, selectivity and sensitivity of DNA biosensors. Thus, DNA biosensors without PCR amplification may become a reality in the foreseeable future.

Prostate Specific Antigen Detection Using Microgapped Electrode Array Immunosensor with Enzymatic Silver Deposition

Background: Analysis of trace proteins plays an essential role in the fields of biomedical research and clinical diagnosis. Development of methods for the detection of proteins at very low concentrations has historically been a challenge in immunochemistry. We have developed an electrical immunosensor for the detection of prostate specific antigen (PSA).

Methods: The electrical immunosensor uses a microgapped interdigitated electrode array (MGIDEA) based on enzymatic silver deposition reaction. The deposition of silver was dispersed over the microgaps and allows the microgapped interdigitated electrodes to be electrically connected, resulting in an increase in electrical conductance of MGIDEA that is used to quantify the analyte concentration. We used this electrical immunosensor to measure PSA in human serum samples from patients with prostate diseases.

Results: This electrical immunosensor exhibited a linear response with PSA concentrations over a 6-decade range from 1.0 pg/L to 1.0 μg/L, with detection limit of 0.9 pg/L. PSA concentrations using this immunosensor agreed within 10% of those obtained using a commercial chemiluminescent immunoassay.

Conclusions: The MGIDEA method has characteristics (analyte specific, low background, low limit of detection) that provide potential for molecular detection in various biomedical areas.

Immobilization and release strategies for DNA delivery using carbon nanofiber arrays and self-assembled monolayers

We report a strategy for immobilizing dsDNA (double-stranded DNA) onto vertically aligned carbon nanofibers and subsequently releasing this dsDNA following penetration and residence of these high aspect ratio structures within cells. Gold-coated nanofiber arrays were modified with self-assembled monolayers (SAM) to which reporter dsDNA was covalently and end-specifically bound with or without a cleavable linker. The DNA-modified nanofiber arrays were then used to impale, and thereby transfect, Chinese hamster lung epithelial cells. This mechanical approach enables the transport of bound ligands directly into the cell nucleus and consequently bypasses extracellular and cytosolic degradation. Statistically significant differences were observed between the expression levels from immobilized and releasable DNA, and these are discussed in relation to the distinct accessibility and mode of action of glutathione, an intracellular reducing agent responsible for releasing the bound dsDNA. These results prove for the first time that an end-specifically and covalently SAM-bound DNA can be expressed in cells. They further demonstrate how the choice of immobilization and release methods can impact expression of nanoparticle delivered DNA.

Synthesis of a virus electrode for measurement of prostate specific membrane antigen

Though relatively unexploited in biosensor applications, phage display technology can provide versatile recognition scaffolds for detection of cancer markers and other analytes. This chapter details protocols for covalent attachment of viruses directly to electrodes for reagent-free detection of analytes in real-time. Customization of binding specificity leverages selections with large phage display libraries prior to covalent attachment of the selected virus to the electrode. The methods described here utilize electrochemical impedance spectroscopy (EIS) to detect molecular recognition between M13 phage bound to a Au electrode and the following analytes: prostate specific membrane antigen (PSMA), positive and negative control antibodies (p-Ab and n-Ab, respectively). Because of a thick layer built on the Au electrode, the real impedance (Zre) increases reliably with S/N ratios upon noncovalent binding to PSMA (approximately 14) and p-Ab (approximately 20).

Protein immobilization on epoxy-activated thin polymer films: effect of surface wettability and enzyme loading

A series of epoxy-activated polymer films composed of poly(glycidyl methacrylate/butyl methacrylate/hydroxyethyl methacrylate) were prepared. Variation in comonomer composition allowed exploration of relationships between surface wettability and Candida antartica lipase B (CALB) binding to surfaces. By changing solvents and polymer concentrations, suitable conditions were developed for preparation by spin-coating of uniform thin films. Film roughness determined by AFM after incubation in PBS buffer for 2 days was less than 1 nm. The occurrence of single CALB molecules and CALB aggregates at surfaces was determined by AFM imaging and measurements of volume. Absolute numbers of protein monomers and multimers at surfaces were used to determine values of CALB specific activity. Increased film wettability, as the water contact angle of films increased from 420 to 550, resulted in a decreased total number of immobilized CALB molecules. With further increases in the water contact angle of films from 55 degrees to 63 degrees, there was an increased tendency of CALB molecules to form aggregates on surfaces. On all flat surfaces, two height populations, differing by more than 30%, were observed from height distribution curves. They are attributed to changes in protein conformation and/or orientation caused by protein-surface and protein-protein interactions. The fraction of molecules in these populations changed as a function of film water contact angle. The enzyme activity of immobilized films was determined by measuring CALB-catalyzed hydrolysis of p-nitrophenyl butyrate. Total enzyme specific activity decreased by decreasing film hydrophobicity.

The use of electrochemical impedance spectroscopy for biosensing

This review introduces the basic concepts and terms associated with impedance and techniques of measuring impedance. The focus of this review is on the application of this transduction method for sensing purposes. Examples of its use in combination with enzymes, antibodies, DNA and with cells will be described. Important fields of application include immune and nucleic acid analysis. Special attention is devoted to the various electrode design and amplification schemes developed for sensitivity enhancement. Electrolyte insulator semiconductor (EIS) structures will be treated separately.

Quantitative electrochemiluminescence detection of proteins: Avidin-based sensor and tris(2,2'-bipyridine) ruthenium(II) label

Quantitative electrochemiluminescence (ECL) detection of a model protein, bovine serum albumin (BSA) was achieved via biotin-avidin interaction using an avidin-based sensor and a well-developed ECL system of tris(2,2'-bipyridine) ruthenium(II) derivative as label and tri-n-propylamine (TPA) as coreactant. To detect the protein, avidin was linked to the glassy carbon electrode through passive adsorptions and covalent interaction with carboxylate-terminated carbon nanotubes that was used as binder to immobilize avidin onto the electrode. Then, biotinylated BSA tagged with tris(2,2'-bipyridine) ruthenium(II) label was attached to the prepared avidin surface. After binding of BSA labeled with tris(2,2'-bipyridine) ruthenium(II) derivative to the surface-immobilized avidin through biotin, ECL response was generated when the self-assembled modified electrode was immersed in a TPA-containing electrolyte solution. Such double protein labeling protocol with a biotin label for biorecognition and ruthenium label for ECL detection facilitated the detection of protein compared to the classical double antibody sandwich format. The ECL intensity was linearly proportional to the feed concentration of BSA over two orders of magnitude in the range of 15nM to 7.5microM. The detection limit was estimated to be 1.5nM. Further application to the lysozyme analysis was carried out to validate the present approach for an effective and favorable protocol for the quantitative detection of proteins. The dynamic range of lysozyme was from 0.001gL(-1) to 0.1gL(-1) and the detection limit was 0.1mgL(-1). Electrochemical impedance and cyclic voltammetric measurements along with some necessary control experiments were conducted to characterize the successful formation of self-assembled modified electrodes and to grant the whole detection process.

Amplified transduction of biomolecular interactions based on the use of nanomaterials

The achievement of very high sensitivity is a major goal in biological assays such as the monitoring of DNA hybridization or protein interactions. This chapter reviews progress in the development of nanomaterials for amplified biosensing and discusses different nanomaterial-based bioamplification strategies. The emergence of nanotechnology is opening new horizons for highly sensitive bioassays and for novel biosensor protocols that employ electronic, optical, or microgravimetric signal transduction. Antibodies or nucleic acids functionalized with metal or semiconductor nanoparticles have been employed as amplifying tags for the biodetection of proteins and DNA. The coupling of different nanomaterial-based amplification platforms and amplification processes dramatically enhances the intensity of the analytical readout and leads to ultrasensitive bioassays. The remarkable sensitivity of the new nanomaterial-based sensing protocols opens up the possibility of detecting disease markers, biothreat agents, or infectious agents that cannot be measured by conventional methods.

Detecting penicillin G in milk with impedimetric label-free immunosensor

A label-free impedimetric flow injection immunosensor for the direct detection of penicillin G has been developed. Anti-penicillin G was immobilized on a gold working electrode modified with a self-assembled monolayer of thioctic acid. Real time monitoring of impedance was carried out at the optimum frequency of 160 Hz. Under optimum operating conditions the system provided a wide linear range between 1.0 x 10(-13) and 1.0 x 10(-8) M with a very low detection limit of 3.0 x 10(-15) M, much lower than the MRL of penicillin G in milk (1.2 x 10(-8) M). The immobilized anti-penicillin G on self-assembled thioctic acid monolayer gold electrode was very stable and provided good reproducible signal after regeneration up to 45 times with a relative standard deviation (R.S.D.) lower than 4%. Good recoveries and precisions were obtained when spiked raw milk samples were analyzed.