Carbon monoxide (CO) is a gaseous mediator, which is generated via anenzymatic reaction of heme oxygenase, and it plays physiological roles in regulating cellular respiration and blood flow in the liver. The concentration and distribution of CO molecules in the living body is unknown owing to a lack of a suitable technique for measuring them in vivo. A needle-type CO sensor has been used for bioinstrumentation, but it is inappropriate for implantation in vivo and long-term monitoring. We developed a CO sensor sheet based on hemoglobin (Hb) allostery, as Hb undergoes a conformational change on CO binding. Hb was extracted from mice blood and mixed with agarose gel with a reducer to stabilize deoxy-Hb in the gel. CO-releasing molecules (CORM) were used to mimic CO-generating tissue, and the sensitivity of the Hb gel could be regulated by Hb concentration. We defined the CO-Hb index, an absorbance ratio at 539 and 557 nm, to estimate the accumulation of captured CO in the gel. It correlatively increased with CORM dose, indicating that gel-embedded Hb underwent a conformational change on CO binding, thereby acting as a CO sensor. We subsequently used the Hb-sensor sheet for two-dimensional imaging of CO distribution. CORM-containing gels with different sizes and doses were layered on this sheet. Size-and dosedependent CO distribution was visualized by scanning the CO-Hb index in the sheet. Our Hb-based CO sensor sheet is composed of biocompatible materials and can be applied to detect low-level CO sources in the living body.
Background Entamoeba histolytica infection is an increasingly common sexually transmitted infection in Japan. Currently, stool ova and parasite examination (O&P) is the only approved diagnostic method. Herein, we assessed the utility of the commercially available rapid antigen detection test (QUIK CHEK) for E. histolytica.
Methods A multicenter cross-sectional study was conducted. Stool samples that had been submitted for O&P examination were included. The samples were subjected to both QUIK CHEK and polymerase chain reaction (PCR), and the QUIK CHEK results were assessed in comparison with PCR as the reference standard.
Results E. histolytica infection was confirmed in 5.8% (38/657) of the samples and comprised 20 diarrheal and 18 non-diarrheal cases. The overall sensitivity and specificity of QUIK CHEK was 44.7% [95% confidence interval 30.1–60.3] and 99.8% [99.1–100], respectively. The sensitivity of QUIK CHEK was higher for diarrheal cases (60.0%) than non-diarrheal cases (27.8%). Further, the combined use of QUIK CHEK with O&P increased the sensitivity (78.9%), especially for diarrheal cases (up to 90%). The E. histolytica burden assessed by quantitative PCR was similar between QUIK CHEK-positive and -negative samples. The QUIK CHEK assay sensitivity was lower for cyst-containing stools than for trophozoite-containing stools, although it was shown that cultured E. histolytica clinical strains from QUIK CHEK-negative cyst-containing stools exhibited antigenicity in vitro.
Conclusions The present study confirmed the high specificity of QUIK CHEK for E. histolytica infection. Combined use with O&P increased the sensitivity of detection, facilitating the use of QUIK CHEK in point-of-care settings in non-endemic situations.
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