Tetrabromobisphenol A (TBBPA) is a flame retardant and has become a widely concerning environmental pollutant. An ultrasensitive nanobody-based immunoassay was developed to monitor the exposure of TBBPA in sediment. First, the anti-TBBPA nanobody was fused with nanoluciferase, and then a one-step bioluminescent enzyme immunoassay (BLEIA) was developed with high sensitivity for TBBPA, with a maximum half inhibition concentration (IC₅₀) at 187 pg/mL. Although approximately 10-fold higher sensitivity can be achieved by this developed BLEIA than by the classical two-step ELISA (IC₅₀ at 1778 pg/mL), it is still a challenge to detect trace TBBPA in sediment samples reliably due to the relatively high matrix effect. To further improve the performance of this one-step BLEIA, a C4b-binding protein (C4BP) was inserted as a self-assembling linker between the nanobody and nanoluciferase. Therefore, a heptamer fusion containing seven binders and seven tracers was generated. This reagent improved the binding capacity and signal amplification. The one-step heptamer plus BLEIA based on this immune-reagent shows an additional 7-fold improvement of sensitivity, with the IC₅₀ of 28.9 pg/mL and the limit of detection as low as 2.5 pg/mL. The proposed assay was further applied to determine the trace TBBPA in sediment, and the recovery was within 92-103%. Taking advantage of this heptamer fusion, one-step BLEIA can serve as a powerful tool for fast detection of trace TBBPA in the sediment samples.

Heavy single-chain antibodies (VHH or nanobodies) are popular in the medical and analytical fields due to its small size, high solubility, stability, and other advantageous features. However, the usage of VHHs is limited by the low yield of its production and purification. In order to determine the optimal purification strategy for VHH to improve the yield, a method to monitor purification at the intermediate steps is needed. In this study, a simple, sensitive, low-cost sandwich enzyme-linked immunosorbent assay (ELISA) was developed to quantitate VHHs throughout the purification steps. Under optimized conditions, the assay has a sensitivity of 0.149 OD·mL/ng and a limit of detection (LOD) of 0.029 ng/mL. The average recoveries of the assay against the spiked samples were 101.9-106.0% and 100.7-108.0%. The method was applied to a variety of real samples for the detection of different VHHs in bacterial cell media. High amount of VHHs (up to 41.3 mg/mL), which are comparable to the average yield of VHH in standard production protocols, were detected in the media. This study raises attention to the problem of protein losses in cell culture supernatants and provides a method for the continuous detection of the protein abundance to optimize the expression and purification protocols especially for nanobodies.

Shifts in the position of the intertropical convergence zone (ITCZ) have great importance for weather, climate, and society. The ITCZ shifts have been extensively studied in current and future warmer climate; however, little is known for its migration in the past on geological time scales. Using an ensemble of climate simulations over the past 540 million years, we show that ITCZ migrations are controlled primarily by continental configuration through two competing pathways: hemispheric radiation asymmetry and cross-equatorial ocean heat transport. The hemispheric asymmetry of absorbed solar radiation is produced mainly by land-ocean albedo contrast, which can be predicted using only the landmass distribution. The cross-equatorial ocean heat transport is strongly associated with the hemispheric asymmetry of surface wind stress, which is, in turn, controlled by the hemispheric asymmetry of ocean surface area. These results allow the influence of continental evolution on global ocean-atmosphere circulations to be understood through simple mechanisms that depend primarily on the latitudinal distribution of land.