A smartphone imaging-based label-free and dual-wavelength fluorescent biosensor with high sensitivity and accuracy

The accuracy of a bioassay based on smartphone-integrated fluorescent biosensors has been limited due to the occurrence of false signals from non-specific reactions as well as a high background and low signal-to-noise ratios for complementary metal oxide semiconductor image sensors. To overcome this problem, we demonstrate dual-wavelength fluorescent detection of biomolecules with high accuracy. Fluorescent intensity can be quantified using dual wavelengths simultaneously, where one decreases and the other increases, as the target analytes bind to the split capture and detection aptamer probes. To do this, we performed smartphone imaging-based fluorescence microscopy using a microarray platform on a substrate with metal-enhanced fluorescence (MEF) using Ag film and Al₂O₃ nano-spacer. The results showed that the sensitivity and specificity of the dual-wavelength fluorescent quantitative assay for the target biomolecule 17-β-estradiol in water were significantly increased through the elimination of false signals. The detection limit was 1pg/mL and the area under the receiver operating characteristic curve of the proposed assay (0.922) was comparable to that of an enzyme-linked immunosorbent assay (0.956) from statistical accuracy tests using spiked wastewater samples. This novel method has great potential as an accurate point-of-care testing technology based on mobile platforms for clinical diagnostics and environmental monitoring.

Integrated Strategies to Gain a Systems-Level View of Dynamic Signaling Networks

In order to survive and function properly in the face of an ever changing environment, cells must be able to sense changes in their surroundings and respond accordingly. Cells process information about their environment through complex signaling networks composed of many discrete signaling molecules. Individual pathways within these networks are often tightly integrated and highly dynamic, allowing cells to respond to a given stimulus (or, as is typically the case under physiological conditions, a combination of stimuli) in a specific and appropriate manner. However, due to the size and complexity of many cellular signaling networks, it is often difficult to predict how cellular signaling networks will respond under a particular set of conditions. Indeed, crosstalk between individual signaling pathways may lead to responses that are nonintuitive (or even counterintuitive) based on examination of the individual pathways in isolation. Therefore, to gain a more comprehensive view of cell signaling processes, it is important to understand how signaling networks behave at the systems level. This requires integrated strategies that combine quantitative experimental data with computational models. In this chapter, we first examine some of the progress that has recently been made toward understanding the systems-level regulation of cellular signaling networks, with a particular emphasis on phosphorylation-dependent signaling networks. We then discuss how genetically targetable fluorescent biosensors are being used together with computational models to gain unique insights into the spatiotemporal regulation of signaling networks within single, living cells.

Facile synthesis of Fe3O4/g-C3N4/HKUST-1 composites as a novel biosensor platform for ochratoxin A

A fluorescent biosensor for ochratoxin A was fabricated on the basis of a new nanocomposite (Fe₃O₄/g-C₃N₄/HKUST-1 composites). Fe₃O₄/g-C₃N₄/HKUST-1 was synthesized in this work for the first time, which combined HKUST-1 with g-C₃N₄ to improve its chemical stability. Fe₃O₄/g-C₃N₄/HKUST-1 composites have strong adsorption capacity for dye-labeled aptamer and are able to completely quench the fluorescence of the dye through the photoinduced electron transfer (PET) mechanism. In the presence of ochratoxin A (OTA), it can bind with the aptamer with high affinity, causing the releasing of the dye-labeled aptamer from the Fe₃O₄/g-C₃N₄/HKUST-1 and therefore results in the recovery of fluorescence. The fluorescence intensity of the biosensor has a linear relationship with the OTA concentration in the range of 5.0-160.0ng/mL. The LOD of sensor is 2.57ng/mL (S/N=3). This fluorescence sensor based on the Fe₃O₄/g-C₃N₄/HKUST-1 composites has been applied to detect OTA in corn with satisfying results.

Fluorescent peptide biosensor for monitoring CDK4/cyclin D kinase activity in melanoma cell extracts, mouse xenografts and skin biopsies

Melanoma constitutes the most aggressive form of skin cancer, which further metastasizes into a deadly form of cancer. The p16(INK4a)-Cyclin D-CDK4/6-pRb pathway is dysregulated in 90% of melanomas. CDK4/Cyclin D kinase hyperactivation, associated with mutation of CDK4, amplification of Cyclin D or loss of p16(INK4a) leads to increased risk of developing melanoma. This kinase therefore constitutes a key biomarker in melanoma and an emerging pharmacological target, however there are no tools enabling direct detection or quantification of its activity. Here we report on the design and application of a fluorescent peptide biosensor to quantify CDK4 activity in melanoma cell extracts, skin biopsies and melanoma xenografts. This biosensor provides sensitive means of comparing CDK4 activity between different melanoma cell lines and further responds to CDK4 downregulation by siRNA or small-molecule inhibitors. By affording means of monitoring CDK4 hyperactivity consequent to cancer-associated molecular alterations in upstream signaling pathways that converge upon this kinase, this biosensor offers an alternative to immunological identification of melanoma-specific biomarkers, thereby constituting an attractive tool for diagnostic purposes, providing complementary functional information to histological analysis, of particular utility for detection of melanoma onset in precancerous lesions. This is indeed the first fluorescent peptide biosensor which has been successfully implemented to monitor kinase activity in skin samples and melanoma tumour xenografts. Moreover by enabling to monitor response to CDK4 inhibitors, this biosensor constitutes an attractive companion assay to identify compounds of therapeutic relevance for melanoma.

Activity Detection of GalNAc Transferases by Protein-Based Fluorescence Sensors In Vivo

Mucin-type O-glycosylation occurring in the Golgi apparatus is an important protein posttranslational modification initiated by up to 20 GalNAc-transferase isozymes with largely distinct substrate specificities. Regulation of this enzyme family affects a vast array of proteins transiting the secretory pathway and misregulation causes human diseases. Here we describe the use of protein-based fluorescence sensors that traffic in the secretory pathway to monitor GalNAc-transferase activity in living cells. The sensors can either be "pan" or isozyme specific.

A fluorescein-labeled AmpC β-lactamase allows rapid characterization of β-lactamase inhibitors by real-time fluorescence monitoring of the β-lactamase-inhibitor interactions

Rapid emergence of class C β-lactamases has urged an immediate need for developing class C β-lactamase specific inhibitors for effective clinical treatment. To facilitate the development of effective class C β-lactamase inhibitors, we propose a new approach for a rapid analysis of the interaction of AmpC β-lactamase and its inhibitors using our recently developed V211Cf fluorescent β-lactamase biosensor during drug screening. Since the fluorescein of V211Cf can report the local environment change in the active site of AmpC β-lactamase, fluorescence responses of V211Cf toward its substrates/inhibitors can provide real-time traces of the dynamic change of the interaction of the β-lactamase with its substrates/inhibitors. In this study, we found that V211Cf displayed distinct fluorescence signal patterns toward different kinds of inhibitors (including clavulanic acid, sulbactam, tazobactam and 2-thiopheneboronic acid) due to the differences in their interactions with β-lactamase. V211Cf not only enables a high throughput screening for inhibitors but can also provide a rapid preliminary indication on the inhibitor's potency and stability to β-lactamase's hydrolytic action as well as how the inhibitors interact with the target enzyme, thereby speeding up the drug discovery and development cycle of class C β-lactamase inhibitors.

A turn-off fluorescent biosensor for the rapid and sensitive detection of uranyl ion based on molybdenum disulfide nanosheets and specific DNAzyme

A novel fluorescent biosensor for detecting uranyl ion (UO2(2+)) in aqueous environment has been developed based on the specific recognition of DNAzyme and the fluorescence quenching ability of molybdenum disulfide (MoS2) nanosheets. The DNAzyme contains a DNA enzyme strand and a 6-carboxylfluorescein (FAM)-labeled DNA substrate strand. We demonstrated that MoS2 nanosheets have low affinity to the substrate-enzyme complex DNAzyme. Whereas, in the presence of UO2(2+), UO2(2+) can specifically cleave DNAzyme to release FAM-labeled single-strand DNA and the released FAM-labeled single-strand DNA can be firmly adsorbed on the surface of MoS2 nanosheets, which resulted in an obvious decrease of fluorescence intensity. This provided a sensing platform for the rapid, simple and sensitive fluorescent detection of UO2(2+). By using the sensing platform, a sensitive and selective fluorescent method for the rapid detection of UO2(2+) has been developed. In comparison with previous biosensor, the proposed method has obvious analytical advantage such as relatively high sensitivity and good stability, short analytical time and low cost. It can be used to detect as low as 2.14 nM of UO2(2+) in aqueous environment with a recovery of 96-102% and a RSD<5% (n=6). The success of this study provides a promising alternative for the rapid and on-site detection of UO2(2+) in environmental monitoring.