Dual-Mode and Label-Free Detection of Exosomes from Plasma Using an Electrochemical Quartz Crystal Microbalance with Dissipation Monitoring

The biomolecular contents of extracellular vesicles, such as exosomes, have been shown to be crucial in intercellular communication and disease propagation. As a result, there has been a recent surge in the exploration of novel biosensing platforms that can sensitively and specifically detect exosomal content such as proteins and nucleic acids, with a view toward application in diagnostic assays. Here, we demonstrate dual-mode and label-free detection of plasma exosomes using an electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D). The platform adopts a direct immunosensing approach to effectively capture exosomes via their surface protein expression of CD63. By combining QCM-D with a tandem in situ electrochemical impedance spectroscopy measurement, we are able to demonstrate relationships between mass, viscoelasticity and impedance inducing properties of each functional layer and analyte. In addition to lowering the limit of detection (by a factor of 2-4) to 6.71 × 107 exosome-sized particles (ESP) per mL in 25% v/v serum, the synergy between dissipation and impedance response introduces improved sensing specificity by offering further distinction between soft and rigid analytes, thereby promoting EQCM-D as an important technique for exosome analysis

Recent developments in biosensing methods for extracellular vesicle protein characterization

Research into extracellular vesicles (EVs) has grown significantly over the last few decades with EVs being widely regarded as a source of biomarkers for human health and disease with massive clinical potential. Secreted by every cell type in the body, EVs report on the internal cellular conditions across all tissue types. Their presence in readily accessible biofluids makes the potential of EV biosensing highly attractive as a noninvasive diagnostic platform via liquid biopsies. However, their small size (50-250 nm), inherent heterogeneity, and the complexity of the native biofluids introduce challenges for effective characterization, thus, limiting their clinical utility. This has led to a surge in the development of various novel EV biosensing techniques, with capabilities beyond those of conventional methods that have been directly transferred from cell biology. In this review, key detection principles used for EV biosensing are summarized, with a focus on some of the most recent and fundamental developments in the field over the last 5 years. This article is categorized under: Diagnostic Tools > Biosensing Diagnostic Tools > In Vitro Nanoparticle-Based Sensing

On the rational design of mesoporous silica humidity sensors

Mesoporous silica is commonly used as matrix for humidity sensors, which operate on the principle of relative humidity-dependent water uptake and read-out by resistive or capacitive means. Although numerous studies have been dedicated to improving the sensing performance, in particular with conductive additives, the effect of pore structure on sensing behaviour has not been systematically investigated so far. Herein, we showcase the effects of pore size and porosity on resistive sensing behaviour in the 0.5-85% relative humidity (RH) range. We employed evaporation-induced self-assembly (EISA) in combination with sol-gel chemistry to fabricate well-defined mesoporous silica thin films with high degree of structural control. Material architectures with pore sizes of 3 to 15 nm and porosities of 40 to 70% were rationally designed by using structure directing agents (SDAs) with increasing molecular weight and tuning the silica to SDA ratio. We found that a combination of pore size of 15 nm and 70% porosity showcases a particularly high sensitivity (~104 times change in resistance) in the measured range, with quick response and recovery times of 3 and 9 seconds, respectively. Across the various sensors, we identified a clear correlation between the pore size and the linear RH sensing range. Sensors with larger mesopores (~15 nm) exhibited higher sensitivity and linear response in the 65 to 85% RH range than sensors with smaller pores (<8 nm). Additionally, increasing the porosity while retaining the pore size, yields better overall sensitivity across the range. Our findings may serve as guidelines for developing broad spectrum high-performance mesoporous sensors and for sensors specifically engineered for optimal operation in specific RH ranges

On the Rational Design of Mesoporous Silica Humidity Sensors

Mesoporous silica is commonly used as matrix for humidity sensors which operate on the principle of relative humidity (RH)-dependent water uptake and read-out by resistance (R) monitoring. Although numerous studies have been dedicated to improving sensitivity with conductive additives, the role of the pore architecture on the sensing behavior has not been systematically investigated so far. Herein, the effects of pore size and porosity on resistive sensing performance in the 0.5–85% RH range are showcased. Across various sensors, a clear correlation is identified between mesopore size and linear RH sensing range. Sensors with larger pores (≈15 nm) exhibit linear response in the 65 to 85% RH range with larger slope (ΔlogR/ΔRH) than sensors with smaller pores (<8 nm). Additionally, increasing porosity while retaining pore size, yields better overall sensor performance across the 15–85% RH range. In particular, a combination of pore size around 15 nm and porosity of 70% showcased a large resistance versus RH response (R0/R ≈ 10000) in the measured range, with quick response and recovery times of 3 and 9 seconds, respectively. These findings may serve as guidelines for developing broad spectrum high performance mesoporous sensors and for sensors specifically engineered to operate in specific RH ranges

Opportunities for isoporous membranes in the manufacture of genomic medicines

Viral and non-viral vectors have revolutionised in the last 5 years the approaches to tackling pandemics, cancers and genetic diseases. The intrinsic properties of these vectors present new separation challenges to their manufacture in terms of both the process-related impurities to be removed and the complex labile nature of the target products. These characteristics make them susceptible to heterogeneity and the formation of product-related impurities. Conventional polyethersulfone membrane filters used for sterile filtration and ultrafiltration of viral vectors and lipid nanoparticles can display limited selectivity and cause product losses. To address these challenges, novel membrane materials and fabrication techniques to overcome the boundary of selectivity-permeability performance have become of interest. Isoporous membranes with well-defined pore size and pore dispersity at the nano-scale show promising separation performance but have only been demonstrated at small scales to date. This review summarises the decision process for the development of new membrane candidates for vector manufacturing in genomic medicine, including membranes fabricated by lithography, track-etched membranes, anodic aluminium oxide (AAO) membranes and self-assembled block copolymer membranes. By comparing these membranes to existing commercially available products, the possible advantages presented by novel materials and fabrication approaches are identified

Glucose Oxidase Loading in Ordered Porous Aluminosilicates: Exploring the Potential of Surface Modification for Electrochemical Glucose Sensing

Enzymatic electrochemical sensors have become the leading glucose detection technology due to their rapid response, affordability, portability, selectivity, and sensitivity. However, the performance of these sensors is highly dependent on the surface properties of the electrode material used to store glucose oxidase and its ability to retain enzymatic activity under variable environmental conditions. Mesoporous thin films have recently attracted considerable attention as promising candidates for enzyme storage and activity preservation due to their well-defined nanoarchitecture and tunable surface properties. Herein, we systematically compare pathways for the immobilization of glucose oxidase (GOx) and their effectiveness in electrochemical glucose sensing, following modification protocols that lead to the electrostatic attraction (amino functionalization), covalent bonding (aldehyde functionalization), and electrostatic repulsion (oxygen plasma treatment) of the ordered porous aluminosilicate-coated electrodes. By direct comparison using a quartz crystal microbalance, we demonstrate that glucose oxidase can be loaded in a nanoarchitecture with a pore size of ∼50 nm and pore interconnections of ∼35 nm using the native aluminosilicate surface, as well as after amino or aldehyde surface modification, while oxygen plasma exposure of the native surface inhibits glucose oxidase loading. Despite a variety of routes for enzyme loading, quantitative electrochemical glucose sensing between 0 and 20 mM was only possible when the porous surface was functionalized with amino groups, which we relate to the role of surface chemistry in accessing the underlying substrate. Our results highlight the impact of rational surface modification on electrochemical biosensing performance and demonstrate the potential of tailoring porous nanoarchitecture surfaces for biosensing applications

Faster Intercalation Pseudocapacitance Enabled by Adjustable Amorphous Titania where Tunable Isomorphic Architectures Reveal Accelerated Lithium Diffusivity

Intercalation pseudocapacitance is a faradaic electrochemical phenomenon with high power and energy densities, combining the attractive features of capacitors and batteries, respectively. Intercalation pseudocapacitive responses exhibit surface-limited kinetics by definition, without restriction from the collective of diffusion-based processes. The surface-limited threshold (SLT) corresponds to the maximum voltage sweep rate (vSLT) exhibiting a predominantly surface-limited current response prior to the onset of diffusion-limitations. Prior studies showed increased lithium diffusivity for amorphous titania compared to anatase. Going beyond prior binary comparisons, here a continuum of amorphous titania configurations were prepared using a series of calcination temperatures to tailor both amorphous character and content. The corresponding amorphous-phase vSLT increased monotonically by 317 % with lowered calcination temperatures. Subsequent isomorphic comparisons varying a single transport parameter at a time identified solid-state lithium diffusion as the dominant diffusive constraint. Thus, performance improvements were linked to increasing the lithium diffusivity of the amorphous phase with decreased calcination temperature. This remarkably enabled 95 % capacity retention (483±17 C/g) with 30 s of delithiation (120 C equivalent). These results highlight how isomorphic sample series can reveal previously unidentified trends by reducing ambiguity and reiterate the potential of amorphization to realize increased performance in known materials

Silica Inverse Opal Nanostructured Sensors for Enhanced Immunodetection of Extracellular Vesicles by Quartz Crystal Microbalance with Dissipation Monitoring

Extracellular vesicles (EVs) are nanosized circulating assemblies that contain biomarkers considered promising for early diagnosis within neurology, cardiology, and oncology. Recently, acoustic wave biosensors, in particular based on quartz crystal microbalance with dissipation monitoring (QCM-D), have emerged as a sensitive, label-free, and selective EV characterization platform. A rational approach to further improving sensing detection limits relies on the nanostructuration of the sensor surfaces. To this end, inorganic inverse opals (IOs) derived from colloidal self-assembly present a highly tunable and scalable nanoarchitecture of suitable feature sizes and surface chemistry. This work systematically investigates their use in two-dimensional (2D) and three-dimensional (3D) for enhanced QCM-D EV detection. Precise tuning of the architecture parameters delivered improvements in detection performance to sensitivities as low as 6.24 × 107 particles/mL. Our findings emphasize that attempts to enhance acoustic immunosensing via increasing the surface area by 3D nanostructuration need to be carefully analyzed in order to exclude solvent and artifact entrapment effects. Moreover, the use of 2D nanostructured electrodes to compartmentalize analyte anchoring presents a particularly promising design principle