A plasmonic nanosensor for lipase activity based on enzyme-controlled gold nanoparticles growth in situ

Paper-Based Distance Sensor for the Detection of Lipase via a Phase Separation-Induced Viscosity Change

Human pancreatic lipase is a symbolic biomarker for the diagnosis of acute pancreatitis, which has profound significance for clinical detection and disease treatment. Herein, we first demonstrate a paper-based lipase sensor via a phase separation-induced viscosity change. Lipase catalyzes triolein to produce oleic acid and glycerol. Adding an excess of Ca²⁺ produces calcium oleate. The remaining Ca²⁺ binds with sodium alginate, triggering hydrogelation with an "egg-box" structure. The viscosity change of the aqueous solution induced by the phase separation process can be quantified by measuring the solution flow distance on a pH test paper. The paper-based lipase sensor has high sensitivity with a detection limit of 0.052 U/mL and also shows excellent specificity. Additionally, it is also utilized for quantitative lipase analysis in human serum samples to exhibit its potency in acute pancreatitis detection. This method overcomes the drawbacks of low sensitivity, slow response, and poor reproducibility caused by the nonuniform distribution of the highly viscous hydrogel on the sensing interface in existing approaches. In conclusion, thanks to the prominent characteristics of high portability, low cost, and easy operation, it is prospective for simple quantitative detection of lipase and has great potential for commercialization.

Phase transfer of fatty acids into ultrasmall nanospheres for colorimetric detection of lipase and albumin

Colorimetric detection of fatty acids during biological interactions is extremely difficult since they are optically silent. Here, fatty acids are found to function as ion-exchangers in ultrasmall polymeric nanospheres to facilitate the protonation of chromoionophores, causing a vivid color change between red and blue. With an excellent detection limit of 1.8 μg mL^-1 for oleic acid, colorimetric assays for lipase and albumin are developed with quick response, high sensitivity, and low cost.

Optimized Immobilization of Biomolecules on Nonspherical Gold Nanostructures for Efficient Localized Surface Plasmon Resonance Biosensing

Plasmonic biosensing techniques employ metal nanostructures, commonly gold (Au), often with biomolecules attached to their surfaces either directly or via other linkers. Various surface chemistry methods based on dispersion and covalent interactions are used to attach biomolecules to Au. As a result, when immobilizing a molecule on a metal surface, quantitative estimates of binding efficiency and stability of these surface chemistry methods are needed. Most prior work to compare such methods deals with bulk/thin film configurations or spherical nanoparticles, and very little is known about immobilization of biomolecules on plasmonic nanostructures of different shapes. Besides, due to rapid advancement of modern nanofabrication techniques, there is a growing need to determine an efficient surface chemistry method for immobilization of biomolecules on nonspherical plasmonic nanostructures. Previous comparison of immobilization methods on spherical Au nanoparticles has shown that physical adsorption resulted in the highest concentration of immobilized antibodies. In our work, we conducted a similar study and compared four representative Au surface functionalization methods as well as estimated how efficient these methods are at attaching biomolecules to nonspherical plasmonic Au nanostructures. We estimated the concentration of immobilized antibody that is specific to human C-reactive protein (anti-hCRP) by measuring the localized surface plasmon resonance (LSPR) shifts after exposing the surface of Au nanostructures to the antibody. Our results differ from the previously reported ones since the highest concentration of anti-hCRP was immobilized using 11-mercaptoundecanoic acid (MUA) chemistry. We demonstrated that immobilized antibodies retained their stability and specificity toward hCRP throughout the immunoassay when diluted hCRP or hCRP-spiked human serum samples were used. These findings have important implications for the fields of biosensing and diagnostics that employ nonspherical plasmonic nanostructures since an overall performance of these devices depends on efficient biomolecule immobilization.

Plasmon-Based Colorimetric Nanosensors for Ultrasensitive Molecular Diagnostics

Colorimetric detection of target analytes with high specificity and sensitivity is of fundamental importance to clinical and personalized point-of-care diagnostics. Because of their extraordinary optical properties, plasmonic nanomaterials have been introduced into colorimetric sensing systems, which provide significantly improved sensitivity in various biosensing applications. Here we review the recent progress on these plasmonic nanoparticles-based colorimetric nanosensors for ultrasensitive molecular diagnostics. According to their different colorimetric signal generation mechanisms, these plasmonic nanosensors are classified into two categories: (1) interparticle distance-dependent colorimetric assay based on target-induced forming cross-linking assembly/aggregate of plasmonic nanoparticles; and (2) size/morphology-dependent colorimetric assay by target-controlled growth/etching of the plasmonic nanoparticles. The sensing fundamentals and cutting-edge applications will be provided for each of them, particularly focusing on signal generation and/or amplification mechanisms that realize ultrasensitive molecular detection. Finally, we also discuss the challenge and give our future perspective in this emerging field.

Nanoparticle-Based and Bioengineered Probes and Sensors to Detect Physiological and Pathological Biomarkers in Neural Cells

Nanotechnology, a rapidly evolving field, provides simple and practical tools to investigate the nervous system in health and disease. Among these tools are nanoparticle-based probes and sensors that detect biochemical and physiological properties of neurons and glia, and generate signals proportionate to physical, chemical, and/or electrical changes in these cells. In this context, quantum dots (QDs), carbon-based structures (C-dots, grapheme, and nanodiamonds) and gold nanoparticles are the most commonly used nanostructures. They can detect and measure enzymatic activities of proteases (metalloproteinases, caspases), ions, metabolites, and other biomolecules under physiological or pathological conditions in neural cells. Here, we provide some examples of nanoparticle-based and genetically engineered probes and sensors that are used to reveal changes in protease activities and calcium ion concentrations. Although significant progress in developing these tools has been made for probing neural cells, several challenges remain. We review many common hurdles in sensor development, while highlighting certain advances. In the end, we propose some future directions and ideas for developing practical tools for neural cell investigations, based on the maxim "Measure what is measurable, and make measurable what is not so" (Galileo Galilei).

A fluorescence nanosensor for lipase activity: enzyme-regulated quantum dots growth in situ

A novel analytical assay to detect the lipase activity was based on the enzyme-regulated quantum dots growth in situ.