Label-free detection of HIV-2 antibodies in serum with an ultra-high frequency acoustic wave sensor

Advances in Electrochemical and Acoustic Aptamer-Based Biosensors and Immunosensors in Diagnostics of Leukemia

Early diagnostics of leukemia is crucial for successful therapy of this disease. Therefore, development of rapid, sensitive, and easy-to-use methods for detection of this disease is of increased interest. Biosensor technology is challenged for this purpose. This review includes a brief description of the methods used in current clinical diagnostics of leukemia and provides recent achievements in sensor technology based on immuno- and DNA aptamer-based electrochemical and acoustic biosensors. The comparative analysis of immuno- and aptamer-based sensors shows a significant advantage of DNA aptasensors over immunosensors in the detection of cancer cells. The acoustic technique is of comparable sensitivity with those based on electrochemical methods; moreover, it is label-free and provides straightforward evaluation of the signal. Several examples of sensor development are provided and discussed.

A Review of Piezoelectric and Magnetostrictive Biosensor Materials for Detection of COVID-19 and Other Viruses

The spread of the severe acute respiratory syndrome coronavirus has changed the lives of people around the world with a huge impact on economies and societies. The development of wearable sensors that can continuously monitor the environment for viruses may become an important research area. Here, the state of the art of research on biosensor materials for virus detection is reviewed. A general description of the principles for virus detection is included, along with a critique of the experimental work dedicated to various virus sensors, and a summary of their detection limitations. The piezoelectric sensors used for the detection of human papilloma, vaccinia, dengue, Ebola, influenza A, human immunodeficiency, and hepatitis B viruses are examined in the first section; then the second part deals with magnetostrictive sensors for the detection of bacterial spores, proteins, and classical swine fever. In addition, progress related to early detection of COVID-19 (coronavirus disease 2019) is discussed in the final section, where remaining challenges in the field are also identified. It is believed that this review will guide material researchers in their future work of developing smart biosensors, which can further improve detection sensitivity in monitoring currently known and future virus threats.

Electromagnetic Piezoelectric Acoustic Sensor Detection of Extracellular Vesicles through Interaction with Detached Vesicle Proteins

An electromagnetic piezoelectric acoustic sensor (EMPAS) was used to study the non-specific adsorption of human red blood cell-derived extracellular vesicle preparations. Vesicle storage history (temperature and duration) highly affected the obtained results: The signal change, namely the frequency decrease of the crystal measured at 20 °C, was negligibly small (<1 s⁻²) when the vesicle solutions had previously been stored at 4 °C, and was in the order of 10 s⁻² when the vesicle solutions had been stored at −30 °C. Moreover, the rate of frequency decrease increased exponentially with the storage time at −30 °C. Upon a 4 °C storage period following the −30 °C storage period of the same sample, the measured frequency decrease dropped, suggesting a partial relaxation of the system. The results are explained by the disintegration of the vesicles triggered by the freeze–thaw cycle, likely due to the detachment of proteins from the vesicle surface as was proved by size-exclusion chromatography. Surface modification of the sensor crystal provided the possibility of signal enhancement, as the maximum rate of the frequency change for the same vesicle concentrations was higher on hydrophobic, octadecyl trichlorosilane–modified quartz than on hydrophilic, bare quartz. The EMPAS signal has been associated with the amount of detached proteins, which in turn is proportional to the originating vesicle concentration.

Advances in Analysis of Milk Proteases Activity at Surfaces and in a Volume by Acoustic Methods

This review is focused on the application of surface and volume-sensitive acoustic methods for the detection of milk proteases such as trypsin and plasmin. While trypsin is an important protein of human milk, plasmin is a protease that plays an important role in the quality of bovine, sheep and goat milks. The increased activity of plasmin can cause an extensive cleavage of β-casein and, thus, affect the milk gelation and taste. The basic principles of surface-sensitive acoustic methods, as well as high-resolution ultrasonic spectroscopy (HR-US), are presented. The current state-of-the-art examples of the application of acoustic sensors for protease detection in real time are discussed. The application of the HR-US method for studying the kinetics of the enzyme reaction is demonstrated. The sensitivity of the acoustics biosensors and HR-US methods for protease detection are compared.

HIV biosensors for early diagnosis of infection: The intertwine of nanotechnology with sensing strategies

Human immunodeficiency virus (HIV) is a lentivirus that leads to acquired immunodeficiency syndrome (AIDS). With increasing awareness of AIDS emerging as a global public health threat, different HIV testing kits have been developed to detect antibodies (Ab) directed toward different parts of HIV. A great limitation of these tests is that they can not detect HIV antibodies during early virus infection. Therefore, to overcome this challenge, a wide range of biosensors have been developed for early diagnosis of HIV infection. A significant amount of these studies have been focused on the application of nanomaterials for improving the sensitivity and accuracy of the sensing methods. Following an introduction into this field, a first section of this review covers the synthesis and applicability of such nanomaterials as metal nanoparticles (NPs), quantum dots (QDs), carbon-based nanomaterials and metal nanoclusters (NCs). A second larger section covers the latest developments concerning nanomaterial-based biosensors for HIV diagnosis, with paying a special attention to the determination of CD4⁺ cells as a hall mark of HIV infection, HIV gene, HIV p24 core protein, HIV p17 peptide, HIV-1 virus-like particles (VLPs) and HIV related enzymes, particularly those that are passed on from the virus to the CD⁴⁺ T lymphocytes and are necessary for viral reproduction within the host cell. These studies are described in detail along with their diverse principles/mechanisms (e.g. electrochemistry, fluorescence, electromagnetic-piezoelectric, surface plasmon resonance (SPR), surface enhanced Raman spectroscopy (SERS) and colorimetry). Despite the significant progress in HIV biosensing in the last years, there is a great need for the development of point-of-care (POC) technologies which are affordable, robust, easy to use, portable, and possessing sufficient quantitative accuracy to enable clinical decision making. In the final section, the focus is on the portable sensing devices as a new standard of POC and personalized diagnostics.

Utilizing a Key Aptamer Structure-Switching Mechanism for the Ultrahigh Frequency Detection of Cocaine

Aptasensing of small molecules remains a challenge as detection often requires the use of labels or signal amplification methodologies, resulting in both difficult-to-prepare sensor platforms and multistep, complex assays. Furthermore, many aptasensors rely on the binding mechanism or structural changes associated with target capture by the aptameric probe, resulting in a detection scheme customized to each aptamer. It is in this context that we report herein a sensitive cocaine aptasensor that offers both real-time and label-free measurement capabilities. Detection relies on the electromagnetic piezoelectric acoustic sensor (EMPAS) platform. The sensing interface consists of a S-(11-trichlorosilyl-undecanyl)benzenethiosulfonate (BTS) adlayer-coated quartz disc onto which a structure-switching cocaine aptamer (MN6) is immobilized, completing the preparation of the MN6 cocaine aptasensor (M6CA). The EMPAS system has recently been employed as the foundation of a cocaine aptasensor based on a structurally rigid cocaine aptamer variant (MN4), an aptasensor referred to by analogy as M4CA. M6CA represents a significant increase in terms of analytical performance, compared to not only M4CA but also other cocaine aptamer-based sensors that do not rely on signal amplification, producing an apparent K(d) of 27 ± 6 μM and a 0.3 μM detection limit. Remarkably, the latter is in the range of that achieved by cocaine aptasensors relying on signal amplification. Furthermore, M6CA proved to be capable not only of regaining its cocaine-binding ability via simple buffer flow over the sensing interface (i.e., without the necessity to implement an additional regeneration step, such as in the case of M4CA), but also of detecting cocaine in a multicomponent matrix possessing potentially assay-interfering species. Finally, through observation of the distinct shape of its response profiles to cocaine injection, demonstration was made that the EMPAS system in practice offers the possibility to distinguish between the binding mechanisms of structure-switching (MN6) vs rigid (MN4) aptameric probes, an ability that could allow the EMPAS to provide a more universal aptasensing platform than what is ordinarily observed in the literature.

Acoustic wave biosensor for the detection of the breast and prostate cancer metastasis biomarker protein PTHrP

There are currently no biosensors that are able to reliably detect the process of cancer metastasis. We describe the first label-free real-time ultra-high frequency acoustic wave biosensor prototype capable of detecting the breast and prostate cancer metastasis biomarker, parathyroid hormone-related peptide (PTHrP). Two different linkers - 11-trichlorosilyl-undecanoic acid pentafluorophenyl ester (PFP) and S-(11-trichlorosilyl-undecanyl)-benzothiosulfonate (TUBTS) - were used to immobilize whole anti-PTHrP antibodies and Fab' fragments to surfaces as biorecognition elements. The biosensor surfaces were optimized using X-ray photoelectron spectroscopy (XPS) and the ultra-high frequency electromagnetic piezoelectric acoustic sensor (EMPAS). One optimized whole antibody-based surface (PFP/protein G'/whole antibodies/ethanolamine) and one optimized Fab' fragment-based surface (TUBTS/Fab' fragments) were tested as biosensors. It was determined that an in-line injection of bovine serum albumin prior to analyte injection yielded the most minimally fouling surfaces. Each surface was tested with no mass amplification and with sandwich-type secondary antibody mass amplification. The whole antibody-based mass-amplified biosensor yielded the lowest limit of detection (61 ng/mL), highest sensitivity, and a linear range from 61 ng/mL to 100 μg/mL. However, the Fab' fragment-based biosensor displayed better regenerability as a loss of ~20% of the initial analyte signal intensity was observed with each subsequent injection. The whole antibody-based biosensor was only capable of producing an analyte signal in the first injection.

Ultra-high frequency piezoelectric aptasensor for the label-free detection of cocaine

This paper describes a label-free and real-time piezoelectric aptasensor for the detection of cocaine. The acoustic wave sensing platform is a quartz substrate functionalized with an adlayer of S-(11-trichlorosilyl-undecanyl)-benzenethiosulfonate (BTS) cross-linker onto which the anti-cocaine MN4 DNA aptamer is next immobilized. Preparation of the sensor surface was monitored using X-ray photoelectron spectroscopy (XPS), while the binding of cocaine to surface-attached MN4 was evaluated using the electromagnetic piezoelectric acoustic sensor (EMPAS). The MN4 aptamer, unlike other cocaine aptamer variants, has its secondary structure preformed in the unbound state with only tertiary structure changes occurring during target binding. It is postulated that the highly sensitive EMPAS detected the binding of cocaine through target mass loading coupled to aptamer tertiary structure folding. The sensor achieved an apparent Kd of 45 ± 12 µM, and a limit of detection of 0.9 µM. Repeated regenerability of the sensor platform was also demonstrated. This work constitutes the first application of EMPAS technology in the field of aptasensors. Furthermore, it is so far one of the very few examples of a bulk acoustic wave aptasensor that is able to directly detect the binding interaction between an aptamer and a small molecule in a facile one-step protocol without the use of a complex assay or signal amplification step.

Critical role of surface hydration on the dynamics of serum adsorption studied with monoethylene glycol adlayers on gold

The dynamics of serum adsorption on bare and monoethylene glycol adlayer-modified gold surfaces is investigated using acoustic wave physics. Hydration experiments support the pivotal role ascribed to water in the antifouling of surfaces. Behavioural discrepancy is interpreted in terms of difference in water structuring properties (surface kosmotropicity).

Rapid detection of human immunodeficiency virus types 1 and 2 by use of an improved piezoelectric biosensor

Disasters can create situations in which blood donations can save lives. However, in emergency situations and when resources are depleted, on-site blood donations require the rapid and accurate detection of blood-borne pathogens, including human immunodeficiency virus types 1 and 2 (HIV-1 and HIV-2). Techniques such as PCR and antibody capture by an enzyme-linked immunosorbent assay (ELISA) for HIV-1 and HIV-2 are precise but time-consuming and require sophisticated equipment that is not compatible with emergency point-of-care requirements. We describe here a prototype biosensor based on piezoelectric materials functionalized with specific antibodies against HIV-1 and HIV-2. We show the rapid and accurate detection of HIV-1 and HIV-2 in both simple and complex solutions, including human serum, and in the presence of a cross-confounding virus. We report detection limits of 12 50% tissue culture infective doses (TCID50s) for HIV-1 and 87 TCID50s for HIV-2. The accuracy, precision of measurements, and operation of the prototype biosensor compared favorably to those for nucleic acid amplification. We conclude that the biosensor has significant promise as a successful point-of-care diagnostic device for use in emergency field applications requiring rapid and reliable testing for blood-borne pathogens.

Surface chemistry to minimize fouling from blood-based fluids

Upon contact with bodily fluids/tissues, exogenous materials spontaneously develop a layer of proteins on their surface. In the case of biomedical implants and equipment, biological processes with deleterious effects may ensue. For biosensing platforms, it is synonymous with an overwhelming background signal that prevents the detection/quantification of target analytes present in considerably lower concentrations. To address this ubiquitous problem, tremendous efforts have been dedicated over the years to engineer protein-resistant coatings. There is now extensive literature available on stealth organic adlayers able to minimize fouling down to a few ng cm(-2), however from technologically irrelevant single-protein buffered solutions. Unfortunately, few coatings have been reported to present such level of performance when exposed to highly complex proteinaceous, real-world media such as blood serum and plasma, even diluted. Herein, we concisely review the surface chemistry developed to date to minimize fouling from these considerably more challenging blood-based fluids. Adsorption dynamics is also discussed.

Single ether group in a glycol-based ultra-thin layer prevents surface fouling from undiluted serum

Through systematic structural modification, it is shown that the internal, single oxygen atom of simple monoethylene glycol-based organic films is essential for radically altering the fouling behaviour of quartz against undiluted serum, as characterized by the electromagnetic piezoelectric acoustic sensor. The synergy is strongest with distal hydroxyls.