Competitive detection of pregnancy-associated plasma protein-A in serum using functional single walled carbon nanotubes/chitosan-based electrochemical immunosensor

Clinical Application of a Graphene Oxide-Based Surface Plasmon Resonance Biosensor to Measure First-Trimester Serum Pregnancy-Associated Plasma Protein-A/A2 Ratio to Predict Preeclampsia

Background

Preeclampsia, a major cause of adverse pregnancy outcomes, involves metalloproteinases pregnancy-associated plasma protein (PAPP)-A and PAPP-A2 from placental trophoblasts. The graphene oxide (GO)-based surface plasmon resonance (SPR) biosensor has higher sensitivity, affinity, and selective ability than the traditional SPR biosensor. The aim of this study was to explore the feasibility of measuring first-trimester serum PAPP-A/PAPP-A2 ratio as a novel predictor of preeclampsia using the GO-SPR biosensor.

Methods

This prospective case-control study of pregnant women was conducted at MacKay Memorial Hospital, Taipei, Taiwan between January 2018 and June 2020. The SPR angle shifts of first-trimester serum PAPP-A, PAPP-A2, and PAPP-A/PAPP-A2 ratio measured using the GO-SPR biosensor were compared between preeclampsia and control groups.

Results

Serum samples from 185 pregnant women were collected, of whom 30 had preeclampsia (5 early-onset; 25 late-onset). The response time between the antibody-antigen association and dissociation only took about 200 seconds. The SPR angle shift of PAPP-A in the preeclampsia group was significantly smaller than that in the control group (median (interquartile range): 5.33 (4.55) versus 6.89 (4.10) millidegrees (mDeg), P = 0.008). Conversely, the SPR angle shift of PAPP-A2 in the preeclampsia group was significantly larger than that in the control group (5.70 (3.81) versus 3.63 (2.38) mDeg, P < 0.001). Receiver operating characteristic (ROC) curve analysis revealed a cut-off PAPP-A/PAPP-A2 ratio to predict all preeclampsia of ≤ 0.76, with an area under the ROC curve (AUC) of 0.79 (95% CI 0.73-0.85, P < 0.001). Sub-group analysis revealed a cut-off PAPP-A/PAPP-A2 ratio to predict early-onset preeclampsia of ≤ 0.53 (AUC 0.99, 95% CI 0.96-1.00, P < 0.001), and ≤ 0.73 to predict late-onset preeclampsia (AUC 0.75, 95% CI 0.68-0.81, P < 0.001).

Conclusion

Measuring first-trimester serum PAPP-A/PAPP-A2 ratio using the GO-SPR biosensor could be a valuable method for early prediction of preeclampsia.

Biosensors for Detection of Human Placental Pathologies: A Review of Emerging Technologies and Current Trends

Substantial growth in the biosensor research has enabled novel, sensitive and point-of-care diagnosis of human diseases in the last decade. This paper presents an overview of the research in the field of biosensors that can potentially predict and diagnosis of common placental pathologies. A survey of biomarkers in maternal circulation and their characterization methods is presented, including markers of oxidative stress, angiogenic factors, placental debris, and inflammatory biomarkers that are associated with various pathophysiological processes in the context of pregnancy complications. Novel biosensors enabled by microfluidics technology and nanomaterials is then reviewed. Representative designs of plasmonic and electrochemical biosensors for highly sensitive and multiplexed detection of biomarkers, as well as on-chip sample preparation and sensing for automatic biomarker detection are illustrated. New trends in organ-on-a-chip based placental disease models are highlighted to illustrate the capability of these in vitro disease models in better understanding the complex pathophysiological processes, including mass transfer across the placental barrier, oxidative stress, inflammation, and malaria infection. Biosensor technologies that can be potentially embedded in the placental models for real time, label-free monitoring of these processes and events are suggested. Merger of cell culture in microfluidics and biosensing can provide significant potential for new developments in advanced placental models, and tools for diagnosis, drug screening and efficacy testing.

Stability and Synergistic Effect of Polyaniline/TiO₂ Photocatalysts in Degradation of Azo Dye in Wastewater

The polyaniline/TiO₂ (PANI/TiO₂) composite photocatalysts were prepared by the in situ chemical oxidation of aniline (An) in the presence of TiO₂ particles. For this purpose, photocatalysts with different amounts of PANI polymer were prepared and analysed. Fourier-transform infrared (FT-IR) spectroscopy and thermogravimetric (TG) analysis indicated successful synthesis of the PANI polymer and its conductivity was also determined. The micrographs of field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) were used to explain the impact of the aniline amount on the aggregation process during the synthesis of the composites. The smallest size of aggregates was obtained for the photocatalysts with 15% of PANI (15PANI/TiO₂) due to the formation of homogenous PANI. The photocatalytic activity of studied PANI/TiO₂ photocatalysts was validated by monitoring the discoloration and mineralization of Reactive Red azo dye (RR45) in wastewater. The 15PANI/TiO₂ sample presented the highest photocatalytic efficiency under ultraviolet A (UVA) irradiation, in comparison to pure TiO₂. This was explained by the formation of uniformly dispersed PANI on the TiO₂ particles, which was responsible for the synergistic PANI-TiO₂ effect.

Prospects of electrochemical immunosensors for early diagnosis of preeclampsia

Preeclampsia is a vascular multisystem disorder that accounts for varying degree of morbidity and mortality of mother and the fetus. This can be significantly averted if diagnosed at an early (18-20 weeks) stage of gestation, as there is no known way to prevent preeclampsia. In spite of extensive work on biomarker discovery, the existing method for its detection is mostly based on colorimetric immunoassays whose sensitivity is ranging in nanomolar range. Further, it has also been observed that change in the expression of a single biomarker is not sufficient to diagnose this condition. So, for early diagnosis (by 18-20 weeks), an immuno-diagnostic platform with detection limits in picomolar range and beyond along with the ability to do simultaneous detection of multiple analyte would be of great importance. A nano-immunosensors with an electrochemical readout system can be a potential alternative that promises for the ultrasensitive detection of analyte with high specificity as well as suitability for on-site analysis. Coupling the lateral flow technology with immunosensors would make it feasible to detect more than one biomarker simultaneously on a microchip. This review intends to summarize the potential preeclampsia biomarkers, limitations of existing diagnostic methods along with the recent advancements, and prospects to develop electrochemical immunosensors for early clinical diagnosis.

Engineered Carbon-Nanomaterial-Based Electrochemical Sensors for Biomolecules

The study of electrochemical behavior of bioactive molecules has become one of the most rapidly developing scientific fields. Biotechnology and biomedical engineering fields have a vested interest in constructing more precise and accurate voltammetric/amperometric biosensors. One rapidly growing area of biosensor design involves incorporation of carbon-based nanomaterials in working electrodes, such as one-dimensional carbon nanotubes, two-dimensional graphene, and graphene oxide. In this review article, we give a brief overview describing the voltammetric techniques and how these techniques are applied in biosensing, as well as the details surrounding important biosensing concepts of sensitivity and limits of detection. Building on these important concepts, we show how the sensitivity and limit of detection can be tuned by including carbon-based nanomaterials in the fabrication of biosensors. The sensing of biomolecules including glucose, dopamine, proteins, enzymes, uric acid, DNA, RNA, and H2O2 traditionally employs enzymes in detection; however, these enzymes denature easily, and as such, enzymeless methods are highly desired. Here we draw an important distinction between enzymeless and enzyme-containing carbon-nanomaterial-based biosensors. The review ends with an outlook of future concepts that can be employed in biosensor fabrication, as well as limitations of already proposed materials and how such sensing can be enhanced. As such, this review can act as a roadmap to guide researchers toward concepts that can be employed in the design of next generation biosensors, while also highlighting the current advancements in the field.

[Cu(phen)2](2+) acts as electrochemical indicator and anchor to immobilize probe DNA in electrochemical DNA biosensor

We demonstrate a novel protocol for sensitive in situ label-free electrochemical detection of DNA hybridization based on copper complex ([Cu(phen)2](2+), where phen = 1,10-phenanthroline) and graphene (GR) modified glassy carbon electrode. Here, [Cu(phen)2](2+) acted advantageously as both the electrochemical indicator and the anchor for probe DNA immobilization via intercalative interactions between the partial double helix structure of probe DNA and the vertical aromatic groups of phen. GR provided large density of docking site for probe DNA immobilization and increased the electrical conductivity ability of the electrode. The modification procedure was monitored by electrochemical impedance spectroscopy (EIS). Square-wave voltammetry (SWV) was used to explore the hybridization events. Under the optimal conditions, the designed electrochemical DNA biosensor could effectively distinguish different mismatch degrees of complementary DNA from one-base mismatch to noncomplementary, indicating that the biosensor had high selectivity. It also exhibited a reasonable linear relationship. The oxidation peak currents of [Cu(phen)2](2+) were linear with the logarithm of the concentrations of complementary target DNA ranging from 1 × 10(-12) to 1 × 10(-6) M with a detection limit of 1.99 × 10(-13) M (signal/noise = 3). Moreover, the stability of the electrochemical DNA biosensor was also studied.