Design and Development of a Field Applicable Gold Nanosensor for the Detection of Luteinizing Hormone

Quantitative detection of pre-ovulatory luteinizing hormone surges in urine using the microfluidic vertical agitation approach

Identifying the time of ovulation is an important process for women seeking and avoiding pregnancy. Luteinizing hormone (LH) plays an important role in ovulation, which is very important in the reproductive mechanism. Therefore, detecting the LH level is of great importance in monitoring ovulation. In this study, sensitive, rapid and selective electrochemical biosensors were developed to detect LH quantitatively from human urine samples and to monitor the ovulation period. Isopotential region and current density optimization studies revealed that sensors with an electrode width and spacing of 1 mm had the optimum performance. Electrochemical impedance spectra evidenced immobilization of DSP self-assembled monolayers and anti-LH-beta antibody on the surface. While the mobile phone vibrator led to a 3.5-fold enhancement in response signals, the agitation system developed resulted in a 10-fold improvement. The sensors displayed detection limits of 1.02 and 1.53 mIU/ml in the range of 0-40 mIU/ml LH concentration obtained using two statistical approaches. Additionally, the sensors showed no cross-reactivity to hCG, which is very similar in structure and is widely reported to have high cross-reactivity.

A dry chemistry-based self-enhanced electrochemiluminescence lateral flow immunoassay sensor for accurate sample-to-answer detection of luteinizing hormone

BACKGROUND

Colorimetric lateral flow immunoassay (LFIA) is a widely used point-of-care testing (POCT) technology, while it has entered a bottleneck period because of low detection sensitivity, expensive preparation materials, and incapable quantitative detection. Therefore, it is necessary to develop a novel POCT method that is ultrasensitive, simple, portable, and capable of accurately detecting biomarkers in biofluids daily, particularly for pregnancy preparation and early screening of diseases.

RESULT

In this work, a novel dry chemistry-based self-enhanced electrochemiluminescence (DC-SE-ECL) LFIA sensor is introduced for accurate POCT of luteinizing hormone (LH). The proposed DC-SE-ECL immunosensor significantly improves the detection sensitivity through the Poly-l-Lysine (PLL)-based SE-ECL probe and cathode modification of closed bipolar electrode (C-BPE). Additionally, a new type of C-BPE configuration is designed for easily performing the LFIA. And, two standalone absorbent pads are symmetrically arranged below the reporting channel of the electrode pad to decease useless residues on the detection pad, which further improves the detection performance. Under optimized conditions, the proposed LFIA sensor has a low limit of detection (9.274 μIU mL-1) and a wide linear dynamic range (0.01-100 mIU mL-1), together with good selectivity, repeatability and storage stability.

SIGNIFICANCE

These results indicate that the proposed DC-SE-ECL method has the potential as a new tool for detecting biomarkers in clinical samples.

Point-of-care impedimetric aptasensor to detect the luteinizing hormone

Luteinizing hormone (LH) is a useful biomarker for identifying ovulation events in the cows to predict the time of ovulation to achieve a high success rate of conception following artificial insemination. Although antibody-based radioimmunoassay and enzyme-linked immunosorbent assay are being used for LH measurement, these techniques are expensive, time-consuming, and require expertise and sophisticated laboratory facilities. So, there is a need for a field-applicable, affordable, easy-to-use method for LH detection. For developing such a specific, quantitative, and inexpensive system, an aptamer-based smartphone-enabled aptasensor has been investigated. The aptamer was used instead of the antibody as a biorecognition element due to its comparative stability at ambient temperature, ease of synthesis, and cost-effectiveness. Electrochemical impedance spectroscopy has been used to obtain label-free detection of LH within 20 min in ~ 20 μL sample volume. The screen-printed gold electrode is compatible with a smartphone-enabled miniaturized device (Sensit Smart; Palmsens BV, The Netherlands) and was fabricated with the aptamer to detect LH in biological fluids (limit of detection 0.80 and 0.61 ng/mL in buffer and undiluted/unprocessed serum, respectively, with the dynamic range of detection of 0.01 to 50 ng/mL). All the data were obtained in the 10 kHz to 0.10 Hz frequency range at a bias potential of 0.30 V with an alternating potential of 10 mV. The clinical relevance of the sensor was evaluated in 10 serum samples collected from dairy animals which established a high correlation with standard LH-ELISA (κ > 0.87). The aptasensor can be stored at room temperature for 30 days without any significant loss in electrochemical sensing ability.

Advanced visual sensing techniques for on-site detection of pesticide residue in water environments

Pesticide usage has increased to fulfil agricultural demand. Pesticides such as organophosphorus pesticides (OPPs) are ubiquitous in world food production. Their widespread usage has unavoidable detrimental consequences for humans, wildlife, water, and soil environments. Hence, the development of more convenient and efficient pesticide residue (PR) detection methods is of paramount importance. Visual detecting approaches have acquired a lot of interest among different sensing systems due to inherent advantages in terms of simplicity, speed, sensitivity, and eco-friendliness. Furthermore, various detections have been proven to enable real-life PR surveillance in environment water. Fluorometric (FL), colourimetric (CL), and enzyme-inhibition (EI) techniques have emerged as viable options. These sensing technologies do not need complex operating processes or specialist equipment, and the simple colour change allows for visual monitoring of the sensing result. Visual sensing techniques for on-site detection of PR in water environments are discussed in this paper. This paper further reviews prior research on the integration of CL, FL, and EI-based techniques with nanoparticles (NPs), quantum dots (QDs), and metal-organic frameworks (MOFs). Smartphone detection technologies for PRs are also reviewed. Finally, conventional methods and nanoparticle (NPs) based strategies for the detection of PRs are compared.

Epitope-based in silico peptide design yields peptide-directed antibodies that recognize the buffalo luteinizing hormone

We present a novel peptide sequence identified through in silico epitope design and the later generation of peptide-directed antibodies recognizing the buffalo luteinizing hormone. Peptides and antibodies, specific to reproductive hormones, are valuable tools for developing point-of-care immunodiagnostic tools. The study predicted an epitope peptide in silico from buffalo luteinizing hormone and the generation of polyclonal antibodies against this peptide sequence. In this quest, we identified a novel epitope peptide sequence (luteinizing hormone peptide, LHP) through bioinformatics tools. The peptide was further synthesized and characterized. The polyclonal antibodies (anti-LHP) were raised against the peptide in the rabbit. Thereafter, we explored a strategy for detecting buffalo luteinizing hormone (LH) using the anti-peptide antibodies developed. The affinity of the peptide, bovine lutropin beta, and crude LH (prepared from buffalo pituitary) towards the raised antibodies was established by dot blot and ELISA. Specific recognition of the luteinizing hormone by the raised polyclonal antibodies highlights the ability of the identified peptide (LHP) and developed polyclonal antibodies (anti-LHP) as suitable diagnostic reagents for sensing the buffalo luteinizing hormone. Through this work, we analyzed and translated the "-omics" information in the LH gene sequence for the development of a novel peptide and antibodies as valuable immuno-reagents.

A proof-of-concept of lateral flow based luteinizing hormone detection in urine for ovulation prediction in buffaloes

We present a method for the detection of luteinizing hormone (LH) in buffalo urine by using gold nanoparticles (AuNPs) conjugated with novel anti-peptide antibodies against LH (anti LHP) in lateral flow assay format. Buffalo LH is an important reproductive hormone and is a chemically complex glycoprotein. Its surge release precedes ovulation and therefore detecting LH has implications in identifying the ovulation event. Any sensor thus developed for sensing LH may have the potential for predicting ovulation and hence can assist herd managers in making decisions on the timing of artificial insemination. Recombinant LH production is time consuming, difficult and costly. Hence, we identified an epitope peptide sequence in buffalo LH and raised antibodies against it. The chemically synthesized peptide and antibodies were used for developing the sensor. The gold nanoparticles and conjugates were characterized through physicochemical methods which confirmed the binding of peptides and antibodies to the gold nanoparticles. A qualitative ELISA for sensing LH was developed based on competitive binding of gold nanoparticles conjugated with the epitope peptide and LH towards the anti-peptide antibodies against LH. We also further explored the detection of LH in buffalo urine using the gold nanoparticle-LHP conjugate (AuNP-LHP) in dipstick format. These experiments provided a proof-of-concept towards applicability of the LH based sensor for ovulation prediction in buffaloes.

Label-free, sensitive colorimetric detection of mercury(II) by target-disturbed in situ seeding growth of gold triangular nanoprisms

Gold nanomaterials have been used extensively in colorimetric detection of mercuric ions (Hg²⁺) due to their shape- and size-dependent, ultrastrong localized surface plasmon resonance (LSPR). Conventional detection was performed by first synthesizing the nanomaterials, and then applying them to signal-transducing reactions. We herein report a convenient method for detecting Hg²⁺ based on gold triangular nanoprisms (AuTNPs). During the seeding-growth process, Hg²⁺ added to the growth solution was co-reduced and deposited on the high-energy facets of the gold seeds, affecting the deposition patterns of the subsequently generated Au⁰ and ultimately leading to the formation of defective AuTNPs. Morphological changes were reflected by the in-plane dipole LSPR wavelength shift, which was proportionally related to the concentration of Hg²⁺. To improve the selectivity, the interference from Ag⁺ was eliminated by a stepwise preparation-selective precipitation approach. Under the optimized conditions, Hg²⁺ could be selectively detected with 20 min, with a detection limit of 0.12 nM. Finally, the method was successfully applied to detecting trace Hg²⁺ in fortified drinking, mineral and rain water samples, with recoveries ranging from 95.17% to 110.6%.

A Combined Aqueous Two-Phase System and Spot-Test Platform for the Rapid Detection of Escherichia coli O157:H7 in Milk

Foodborne illnesses are a public health concern in the United States and worldwide. Recent outbreaks of Escherichia coli O157:H7 have brought to light the need for improved ways to detect foodborne pathogens and minimize serious outbreaks. Unfortunately, current methods for the detection of foodborne pathogens are time intensive and complex. In this study, we designed a spot immunoassay that uses a UCON-potassium phosphate salt aqueous two-phase system (ATPS) for the preconcentration of O157:H7. This platform was tested with samples of O157:H7 spiked in phosphate-buffered saline and milk. The ATPS was found to improve the detection limit of the spot test, yielding detection at 106 cfu/mL within 30 min. This is the first known application of ATPSs to spot immunoassays. Moreover, detection was successfully achieved without upstream processing or dilution of the sample prior to testing, thereby further simplifying the detection process. This technology’s ease of use, sensitivity, and short time to result highlight its potential to advance the spot test as a viable diagnostic tool for foodborne pathogens.

Paper-based sensors and assays: a success of the engineering design and the convergence of knowledge areas

This review shows the recent advances and state of the art in paper-based analytical devices (PADs) through the analysis of their integration with microfluidics and LOC micro- and nanotechnologies, electrochemical/optical detection and electronic devices as the convergence of various knowledge areas. The important role of the paper design/architecture in the improvement of the performance of sensor devices is discussed. The discussion is fundamentally based on μPADs as the new generation of paper-based (bio)sensors. Data about the scientific publication ranking of PADs, illustrating their increase as an experimental research topic in the past years, are supplied. In addition, an analysis of the simultaneous evolution of PADs in academic lab research and industrial commercialization highlighting the parallelism of the technological transfer from academia to industry is displayed. A general overview of the market behaviour, the leading industries in the sector and their commercialized devices is given. Finally, personal opinions of the authors about future perspectives and tendencies in the design and fabrication technology of PADs are disclosed.

Three-Dimensional Nanocomposites: Fluidics Driven Assembly of Metal Nanoparticles on Protein Nanostructures and Their Cell-Line-Dependent Intracellular Trafficking Pattern

Three-dimensional nanocomposites prepared using two different families of nanomaterials holds significant relevance pertaining to biological applications. However, integration of the two distinct nanomaterials with precision to control the overall compositional homogeneity of the resulting 3D nanocomposite is a synthetic challenge. Conventional reactions result in nanocomposites with heterogeneous composition and render useless. To address this challenge, we have developed a fluidics-mediated process for controlling the interaction of nanoparticles to yield a compositional uniform multidimensional nanoparticle; as an example, we demonstrated the integration of gold nanoparticles on gelatin nanoparticles. The composition of the nanocomposite is controlled by reacting predetermined number of gold nanoparticles to a known number of thiolated gelatin nanoparticles at any given time within a defined cross-sectional area. Using the fluidics process, we developed nanocomposites of different composition: [gelatin nanoparticles-(gold nanoparticles)x] where xaverage = 2, 12, or 25. The nanocomposites were further surface conjugated with organic molecules such as fluorescent dye or polyethylene glycol (PEG) molecules. To study the biological behavior of nanocomposite, we investigated the cellular internalization and trafficking characteristics of nanocomposites in two human cancer cell lines. The nanocomposites exhibited a three-stage cellular release mechanism that enables the translocation of gold nanoparticles within various cellular compartments. In summary, the three-dimensional nanocomposite serves as a novel platform for developing well-defined protein-metal nanocomposites for potential drug delivery, sensory, and molecular imaging applications.

Interactions between bacterial surface and nanoparticles govern the performance of "chemical nose" biosensors

Rapid and portable diagnosis of pathogenic bacteria can save lives lost from infectious diseases. Biosensors based on a "chemical nose" approach are attracting interest because they are versatile but the governing interactions between bacteria and the biosensors are poorly understood. Here, we use a "chemical nose" biosensor based on gold nanoparticles to explore the role of extracellular polymeric substances in bacteria-nanoparticle interactions. We employ simulations using Maxwell-Garnett theory to show how the type and extent of aggregation of nanoparticles influence their colorimetric response to bacteria. Using eight different species of Gram-positive and Gram-negative bacteria, we demonstrate that this "chemical nose" can detect and identify bacteria over two orders of magnitude of concentration (89% accuracy). Additionally, the "chemical nose" differentiates between binary and tertiary mixtures of the three most common hospital-isolated pathogens: Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa (100% accuracy). We demonstrate that the complex interactions between nanoparticles and bacterial surface determine the colorimetric response of gold nanoparticles and thus, govern the performance of "chemical nose" biosensors.

A paper based microfluidic device for easy detection of uric acid using positively charged gold nanoparticles

A paper based microfluidic device is fabricated that can rapidly detect very low concentrations of uric acid (UA) using 3,5,3',5'-tetramethyl benzidine (TMB), H2O2 and positively charged gold nanoparticles ((+)AuNPs). In the presence of (+)AuNPs, H2O2 reacts with TMB to produce a bluish-green colour which becomes colourless on reaction with UA. This colorimetric method can detect as low as 8.1 ppm of UA within <20 minutes on white filter paper. This technique provides an alternative way for UA detection.

Smart gold nanosensor for easy sensing of lead and copper ions in solution and using paper strips

A smart gold nanosensor, Au–TA–DNS is designed that can rapidly detect very low concentrations of Pb²⁺ and Cu²⁺ ions.