Retraction: A new polymer lab-on-a-chip (LOC) based on a microfluidic capillary flow assay (MCFA) for detecting unbound cortisol in saliva.

Retraction of 'A new polymer lab-on-a-chip (LOC) based on a microfluidic capillary flow assay (MCFA) for detecting unbound cortisol in saliva' by Vinitha T. U. et al., Lab Chip, 2020, 20, 1961-1974, DOI: https://doi.org/10.1039/D0LC00071J.

Lab on a chip for detecting Clara cell protein 16 (CC16) for potential screening of the workers exposed to respirable silica aerosol.

Early detection of pulmonary responses to silica aerosol exposure, such as lung inflammation as well as early identification of silicosis initiation, is of great importance in disease prevention of workers. In this study, to early screen the health condition of the workers who are exposed to respirable silica dusts, an immunoassay lab on a chip (LOC) was designed, developed and fully characterized for analyzing Clara cell protein 16 (CC16) in serum which has been considered as one of the potential biomarkers of lung inflammation or lung damage due to the respirable silica dusts. Sandwich immunoassay of CC16 was performed on the LOC developed with a custom-designed portable analyzer using artificial serums spiked with CC16 protein first and then human serums obtained from the coal mine workers exposed to the respirable silica-containing dusts. The dynamic range of CC16 assay performed on the LOC was in a range of 0.625-20 ng/mL, and the achieved limit of detection (LOD) was around 0.35 ng/mL. The assay results of CC16 achieved from both the developed LOC and the conventional 96 well plate showed a reasonable corelation. The correlation between the conventional reader and the developed portable analyzer was found to be reasonable, resulting in R2 ~ 0.93. This study shows that the LOC developed for the early detection of CC16 can be potentially applied for the development of a field-deployable point-of-care testing (POCT) for the early monitoring of the field workers who are exposed to silica aerosol.

A new polymer lab-on-a-chip (LOC) based on a microfluidic capillary flow assay (MCFA) for detecting unbound cortisol in saliva.

Unbound cortisol in saliva, which can be detected with non-invasive sampling, is now considered as one of the most effective biomarkers for the biochemical evaluation of common mental disorders. In this work, a new polymer lab-on-a-chip (LOC) based on a microfluidic capillary flow assay (MCFA) with on-chip dried reagents was newly developed and fully characterized for the detection of unbound cortisol in saliva. The new MCFA device consisted of serially connected microchannels for sample loading, dried detection antibodies, time delay for incubation time control, a spiral reaction chamber for testing, positive and negative controls, and a capillary pump for waste fluid collection. In addition, a portable fluorescence analyzer was also developed for the rapid quantitative measurement of salivary cortisol with high accuracy. A linear dynamic range of 7.0 pg mL-1-16.0 ng mL-1 was achieved from spiked artificial saliva samples with an inter-chip CV of around 4.0% using the developed LOC and fluorescence analyzer. The achieved results support the effective biochemical analysis of common mental disorders such as chronic stress, depression, anxiety and post traumatic stress disorder (PTSD). The new LOC based on a microfluidic capillary flow assay (MCFA) developed in this work can be one of the most promising LOC platforms for high-sensitivity and quantitative POCT with saliva and blood plasma/serum samples.

A new microchannel capillary flow assay (MCFA) platform with lyophilized chemiluminescence reagents for a smartphone-based POCT detecting malaria.

There has been a considerable development in microfluidic based immunodiagnostics over the past few years which has greatly favored the growth of novel point-of-care-testing (POCT). However, the realization of an inexpensive, low-power POCT needs cheap and disposable microfluidic devices that can perform autonomously with minimum user intervention. This work, for the first time, reports the development of a new microchannel capillary flow assay (MCFA) platform that can perform chemiluminescence based ELISA with lyophilized chemiluminescent reagents. This new MCFA platform exploits the ultra-high sensitivity of chemiluminescent detection while eliminating the shortcomings associated with liquid reagent handling, control of assay sequence and user intervention. The functionally designed microchannels along with adequate hydrophilicity produce a sequential flow of assay reagents and autonomously performs the ultra-high sensitive chemiluminescence based ELISA for the detection of malaria biomarker such as PfHRP2. The MCFA platform with no external flow control and simple chemiluminescence detection can easily communicate with smartphone via USB-OTG port using a custom-designed optical detector. The use of the smartphone for display, data transfer, storage and analysis, as well as the source of power allows the development of a smartphone based POCT analyzer for disease diagnostics. This paper reports a limit of detection (LOD) of 8 ng/mL by the smartphone analyzer which is sensitive enough to detect active malarial infection. The MCFA platform developed with the smartphone analyzer can be easily customized for different biomarkers, so a hand-held POCT for various infectious diseases can be envisaged with full networking capability at low cost.

Highly Sensitive Lab on a Chip (LOC) Immunoassay for Early Diagnosis of Respiratory Disease Caused by Respirable Crystalline Silica (RCS).

Respirable crystalline silica (RCS) produced in mining and construction industries can cause life-threatening diseases such as silicosis, lung cancer, and chronic obstructive pulmonary disease (COPD). These diseases could be more effectively treated and prevented if RCS-related biomarkers were identified and measured at an early stage of disease progression, which makes development of a point of care test (POCT) platform extremely desirable for early diagnosis. In this work, a new, highly sensitive lab on a chip (LOC) immunoassay has been designed, developed, and characterized for tumor necrosis factor α (TNF-α), a protein biomarker that causes lung inflammation due to RCS exposure. The designed LOC device is composed of four reservoirs for sample, enzyme conjugated detection antibody, wash buffer, and chemiluminescence substrate in liquid form, along with three spiral reaction chambers for test, positive control, and negative control. All reservoirs and spiral microchannels were connected in series and designed to perform sequential delivery of immunoassay reagents with minimal user intervention. The developed LOC measured TNF-α concentrations as low as 16 pg/mL in plasma from RCS-exposed rats and also had a limit of detection (LOD) of 0.5 pg/mL in spiked artificial serum. In addition, the analysis time was drastically reduced to about 30 min, as opposed to hours in conventional methods. Successful implementation of a highly sensitive, chemiluminescence-based immunoassay on a preloaded LOC with proper quality control, as reported in this work, can pave the way toward developing a new rapid POCT platform for in-field clinical diagnosis.

Lyophilization of chemiluminescent substrate reagents for high-sensitive microchannel-based lateral flow assay (MLFA) in point-of-care (POC) diagnostic system.

Over the last few years, lateral flow assay (LFA) devices have grown to be the most common point-of-care test (POCT) platform facilitating disease diagnostics in low-resource environments. However, the lack of consistency and the limited sensitivity of these devices often lead to misdiagnosis and generates the need for an alternate approach. A chemiluminescence based microchannel-based lateral flow assay (MLFA) in a POCT platform can result in a much higher sensitivity but involves multiple additional steps of liquid reagents for the sequential execution of the signal amplification protocol. One of the best ways to develop a sample-to-answer system with minimum user intervention is to dry reagents on a chip prior to sample addition and to control the flow of the biological fluid through the drying chambers resulting in the reconstitution of the reagents. This work reports the methods for the successful lyophilization of the chemiluminescent substrate and its reconstitution in artificial serum without any significant loss of functionality. The lyophilized reagents were reconstituted and incorporated into the reaction chambers of a designed polymer lab-on-a-chip to implement a sandwich assay for the detection of malarial biomarkers. The results report a limit of detection (LOD) of 5.75 ng mL-1 which is sensitive enough to detect active malarial infection. Successful lyophilization and reconstitution of the chemiluminescent substrate, as reported here, can pave the way towards developing an autonomous POCT system implementing chemiluminescence based sandwich ELISA for enhanced sensitivity, portability, and ease-of-use in resource limited settings.

Pathogen-specific DNA sensing with engineered zinc finger proteins immobilized on a polymer chip.

A specific double-stranded DNA sensing system is of great interest for diagnostic and other biomedical applications. Zinc finger domains, which recognize double-stranded DNA, can be engineered to form custom DNA-binding proteins for the recognition of specific DNA sequences. As a proof of concept, a sequence-enabled reassembly of a TEM-1 ß-lactamase system (SEER-LAC) was previously demonstrated to develop zinc finger protein (ZFP) arrays for the detection of a double-stranded bacterial DNA sequence. Here, we implemented the SEER-LAC system to demonstrate the direct detection of pathogen-specific DNA sequences present in E. coli O157:H7 on a lab-on-a-chip. ZFPs custom-designed to detect Shiga toxin in E. coli O157:H7 were immobilized on a cyclic olefin copolymer (COC) chip, which can function as a non-PCR based molecular diagnostic device. Pathogen-specific double-stranded DNA was directly detected by using engineered ZFPs immobilized on the COC chip with high specificity, providing a detection limit of 10 fmol of target DNA in a colorimetric assay. Therefore, in this study, we demonstrated the great potential of ZFP arrays on the COC chip for further development of a simple and novel lab-on-a-chip technology for the detection of pathogens.