Advances on microfluidic paper-based electroanalytical devices

Since the inception of the first electrochemical devices on paper substrates, many different reports of microfluidic paper-based electroanalytical devices (μPEDs), innovative hydrophobic barriers and electrode fabrication processes have allowed the incorporation of diverse materials, resulting in different applications and a boost in performance. These advancements have led to the creation of paper-based devices with comparable performance to many standard conventional devices, with the added benefits of pumpless fluidic transport, component separation and reagent storage that can be exploited to automate and handle sample preprocessing. Herein, we review μPEDs, summarize the characteristics and functionalities of μPEDs, such as separation, fluid flow control and storage, and outline the conventional and emerging fabrication and modification approaches for μPEDs. We also examine the recent application of μPEDs in biomedicine, the environment, and food and water safety, as well as some limitations and challenges that must be addressed.

Pressure-based beat-to-beat right ventricular ejection fraction and Tau from continuous measured ventricular pressures in COVID-19 ARDS patients

We evaluated pressure-based right ventricular ejection fraction (RVEF) and diastolic isovolumetric relaxation time constant (Tau) from continuously (up to 30 days) invasive measured right ventricular pressures in mechanically ventilated patients with severe COVID-19 acute respiratory distress syndrome (ARDS). We retrospectively calculated beat-to-beat ejection fraction from right ventricular pressures and dp/dt maximum and minimum in 39 patients treated between October 1st, 2020 and June 30th, 2021. After performing a stepwise logistic regression with survival as a dependent variable, we divided the patients into survivors and nonsurvivors based on their 60-day mortality. Independent outcome variables were the values of RVEF and Tau over time after insertion of the right ventricular probe along with right ventricular systolic and diastolic pressures (RVSP) and the estimated pulmonary artery diastolic pressure (ePAD). RVEF increased significantly over time in the survivors (estimate: 0.354; 95% confidence interval, CI: 0.18-0.53; p < 0.001) but remained unchanged in the nonsurvivors. Tau increased significantly in the nonsurvivors (estimate: 0.001; 95% CI: 0.0004-0.0018; p < 0.002) but not in the survivors. On the last measurement day, RVSP and ePAD were significantly lower while RVEF was significantly higher in the survivors compared to the nonsurvivors. In COVID-19 ARDS patient's, calculation of beat-to-beat RVEF and Tau from continuously invasive measured right ventricular pressures seems to unravel contrary trends in RVEF with an increase in the surviving and a decrease in the nonsurviving patients. Tau remained unchanged in the surviving but increased in the nonsurviving patients over time.

Disposable Paper-Based Biosensors: Optimizing the Electrochemical Properties of Laser-Induced Graphene

Laser-induced graphene (LIG) on paper substrates is a desirable material for single-use point-of-care sensing with its high-quality electrical properties, low fabrication cost, and ease of disposal. While a prior study has shown how the repeated lasing of substrates enables the synthesis of high-quality porous graphitic films, however, the process-property correlation of lasing process on the surface microstructure and electrochemical behavior, including charge-transfer kinetics, is missing. The current study presents a systematic in-depth study on LIG synthesis to elucidate the complex relationship between the surface microstructure and the resulting electroanalytical properties. The observed improvements were then applied to develop high-quality LIG-based electrochemical biosensors for uric acid detection. We show that the optimal paper LIG produced via a dual pass (defocused followed by focused lasing) produces high-quality graphene in terms of crystallinity, sp² content, and electrochemical surface area. The highest quality LIG electrodes achieved a high rate constant k₀ of 1.5 × 10^-2 cm s^-1 and a significant reduction in charge-transfer resistance (818 Ω compared with 1320 Ω for a commercial glassy carbon electrode). By employing square wave anodic stripping voltammetry and chronoamperometry on a disposable two-electrode paper LIG-based device, the improved charge-transfer kinetics led to enhanced performance for sensing of uric acid with a sensitivity of 24.35 ± 1.55 μA μM^-1 and a limit of detection of 41 nM. This study shows how high-quality, sensitive LIG electrodes can be integrated into electrochemical paper analytical devices.

Paper-Based Electrodes Conjugated with Tungsten Disulfide Nanostructure and Aptamer for Impedimetric Detection of Listeria monocytogenes

In this study, we report on a novel aptasensor based on an electrochemical paper-based analytical device (ePAD) that employs a tungsten disulfide (WS₂)/aptamer hybrid for the detection of Listeria monocytogenes. Listeria is a well-known causative pathogen for foodborne diseases. The proposed aptasensor signifies many lucrative features which include simple, cost-effective, reliable, and disposable. Furthermore, the use of an aptamer added more advantageous features in the biosensor. The morphological, optical, elemental composition, and phase properties of the synthesized tungsten disulfide (WS₂) nanostructures were characterized by field-emission scanning electron microscopy (FESEM), RAMAN spectroscopy, photoluminescence (PL), and X-ray diffraction (XRD), while electrochemical impedance spectroscopy was performed to corroborate the immobilization of aptamer and to assess the L. monocytogenes sensing performance. The limit of detection (LoD) and limit of quantification (LoQ) of the aptasensor was found to be 10 and 4.5 CFU/mL, respectively, within a linear range of 10¹-10⁸ CFU/mL. The proposed sensor was found to be selective solely towards Listeria monocytogenes in the presence of various bacterial species such as Escherichia coli and Bacillus subtilis. Validation of the aptasensor operation was also evaluated in real samples by spiking them with fixed concentrations (10¹, 10³, and 10⁵) of Listeria monocytogenes, thereby, paving the way for its potential in a point-of-care scenario.

Continuous long-term wireless measurement of right ventricular pressures and estimated diastolic pulmonary artery pressure in patients with severe COVID-19 acute respiratory distress syndrome

Aims

We continuously monitored right ventricular pressures and the estimated diastolic pulmonary artery pressure (ePAD) for up to 30 days in mechanically ventilated patients with severe COVID‐19 acute respiratory distress syndrome in order to detect and treat right ventricular and pulmonary artery hypertension.

Methods and Results

We retrospectively evaluated right ventricular pressures and the ePAD measured in 30 invasively ventilated COVID‐19 acute respiratory distress syndrome patients between 1 October 2020 and 31 March 2021. We divided the patients into two groups, survivors and non‐survivors based on their 60 day mortality. Primary outcome variables were the values of right ventricular pressures and the ePAD over time after insertion of the right ventricular probe.

Right ventricular systolic pressure [RVSP, (IQR; 25th to 75th percentile)] was significantly lower on the first and the last measurement day in the survivors compared with the non‐survivors [Day 1: 38 (27–45) vs. 46 (44–49), P = 0.036; last day: 36 (27–44) vs. 51 (40–57) mmHg, P = 0.006]. 16/22 survivors and 7/8 non‐survivors received sildenafil orally, one survivor received additionally inhaled nitric oxide and one survivor and one non‐survivor each inhaled iloprost. On the last measurement day, both right ventricular pressure amplitude [31 (26–37) vs. 38 (35–47) mmHg, P = 0.027] and ePAD [22 (16–26) vs. 31 (23–34) mmHg, P = 0.043] were significantly lower in the survivors compared with the non‐survivors. Four patients in the survivor group developed excessive high RVSP in the course of their disease (peak: 57/61/78/105 mmHg). After sildenafil 20 mg every 8 h, additional inhaled nitric oxide (20 ppm) in one and additional inhaled iloprost 20 μg every 4 h in another patient RVSP consecutively decreased substantially in all four patients until the end of the measurement period (47/23/42/47 mmHg).

Conclusions

The RVSP and right ventricular pressure amplitude both were significantly lower in the survivors compared with those in the non‐survivors with a significant decrease in RVSP over time in the survivors suggesting successful lowering by pulmonary vasodilators. The ePAD as an indicator of left heart failure was significantly higher in non‐survivors compared to the surviving patients.

Alcohol-Triggered Capillarity through Porous Pyrolyzed Paper-Based Electrodes Enables Ultrasensitive Electrochemical Detection of Phosphate

The sensing field has shed light on an urgent necessity for field-deployable, user-friendly, sensitive, and scalable platforms that are able to translate solutions into the real world. Here, we attempt to meet these requests by addressing a simple, low-cost, and fast electrochemical approach to provide sensitive assays that consist of dropping a small volume (0.5 μL) of off-the-shelf alcohols on pyrolyzed paper-based electrodes before adding the sample (150 μL). This method was applied in the detection of phosphate after the formation of the phosphomolybdate complex (250-860 nm in size). Prior drops of isopropanol allow for the fast penetration of the sample through pores of this hydrophobic paper, delivering hindrance-free redox reactions across increasing active areas and ultimately improving the detection performance. The sensitivity (-1.9 10^-6 mA cm^-2 ppb^-1) and limit of detection (1.1 ppb) were improved, respectively, by factors of 33 and 99 over the data achieved without the addition of isopropanol, listing among the lowest values when compared with those results reported in the literature for phosphate (expressed in terms of the concentration of phosphorus). The approach enabled the quantification of this analyte in real samples with accuracies ranging from 87 to 103%. Furthermore, preliminary measurements demonstrated the successful performance of the electrodes with prior addition of other widely used alcohols, that is, methanol and ethanol. These results may extend the applicability of the method. In special, the scalability and eco-friendly character of the electrode fabrication combined with the sensitivity and simplicity of the analyses make the developed platform a promising alternative that may help to pave the way for a new generation of disposable sensors toward the daily monitoring of phosphate in water samples, thus contributing to prevent ecological side effects.

Automatic Staging of Cancer Tumors Using AIM Image Annotations and Ontologies

A second opinion about cancer stage is crucial when clinicians assess patient treatment progress. Staging is a process that takes into account description, location, characteristics, and possible metastasis of tumors in a patient. It should follow standards, such as the TNM Classification of Malignant Tumors. However, in clinical practice, the implementation of this process can be tedious and error prone. In order to alleviate these problems, we intend to assist radiologists by providing a second opinion in the evaluation of cancer stage. For doing this, we developed a TNM classifier based on semantic annotations, made by radiologists, using the ePAD tool. It transforms the annotations (stored using the AIM format), using axioms and rules, into AIM4-O ontology instances. From then, it automatically calculates the liver TNM cancer stage. The AIM4-O ontology was developed, as part of this work, to represent annotations in the Web Ontology Language (OWL). A dataset of 51 liver radiology reports with staging data, from NCI's Genomic Data Commons (GDC), were used to evaluate our classifier. When compared with the stages attributed by physicians, the classifier stages had a precision of 85.7% and recall of 81.0%. In addition, 3 radiologists from 2 different institutions manually reviewed a random sample of 4 of the 51 records and agreed with the tool staging. AIM4-O was also evaluated with good results. Our classifier can be integrated into AIM aware imaging tools, such as ePAD, to offer a second opinion about staging as part of the cancer treatment workflow.

Building and Querying RDF/OWL Database of Semantically Annotated Nuclear Medicine Images

As the use of positron emission tomography-computed tomography (PET-CT) has increased rapidly, there is a need to retrieve relevant medical images that can assist image interpretation. However, the images themselves lack the explicit information needed for query. We constructed a semantically structured database of nuclear medicine images using the Annotation and Image Markup (AIM) format and evaluated the ability the AIM annotations to improve image search. We created AIM annotation templates specific to the nuclear medicine domain and used them to annotate 100 nuclear medicine PET-CT studies in AIM format using controlled vocabulary. We evaluated image retrieval from 20 specific clinical queries. As the gold standard, two nuclear medicine physicians manually retrieved the relevant images from the image database using free text search of radiology reports for the same queries. We compared query results with the manually retrieved results obtained by the physicians. The query performance indicated a 98 % recall for simple queries and a 89 % recall for complex queries. In total, the queries provided 95 % (75 of 79 images) recall, 100 % precision, and an F1 score of 0.97 for the 20 clinical queries. Three of the four images missed by the queries required reasoning for successful retrieval. Nuclear medicine images augmented using semantic annotations in AIM enabled high recall and precision for simple queries, helping physicians to retrieve the relevant images. Further study using a larger data set and the implementation of an inference engine may improve query results for more complex queries.