Fluorescent dyes have enabled much progress in the broad range of biomedical fields. However, many commercially available dyes suffer from small Stokes shifts, resulting in poor signal-to-noise ratio and self-quenching on current microscope configurations. In this work, we have developed a general method to significantly increase the Stokes shifts of common fluorophores. By simply appending a 1,4-diethyl-decahydro-quinoxaline (DQ) moiety onto the conjugated structure, we introduced a vibronic backbone that could facilely expand the Stokes shifts, emission wavelength, and photostability of 11 different fluorophores by more than 3-fold. This generalizable method could significantly improve the imaging efficiency of commercial fluorophores. As a demonstration, we showed that the DQ derivative of hemicyanine generated 5-fold signal in mouse models over indocyanine green. Furthermore, the DQ-modified fluorophores could pair with their parent molecules to conduct one-excitation, multiple emission imaging, allowing us to study the cell behavior more robustly. This approach shows promise in generating dyes suitable for super-resolution microscopy and second window near-infrared imaging.

Organic dye based NIR‐II fluorescent probes, owing to their high signal‐to‐background ratio and deeper penetration, are highly useful for deep‐tissue high‐contrast imaging in vivo. However, it is still a challenge to design activatable NIR‐II fluorescent probes. Here, a novel class of polymethine dyes (NIRII‐RTs), with bright (quantum yield up to 2.03 %), stable, and anti‐solvent quenching NIR‐II emission, together with large Stokes shifts, was designed. Significantly, the novel NIR‐II dyes NIRII‐RT3 and NIRII‐RT4, equipped with a carboxylic acid group, can serve as effective NIR‐II platforms for the design of activatable bioimaging probes with high contrast. As a proof of concept, a series of target‐activatable NIRII‐RT probes (NIRII‐RT‐pH, NIRII‐RT‐ATP and NIRII‐RT‐Hg) for pH, adenosine triphosphate (ATP), and metal‐ion detection, were synthesized. By applying the NIRII‐RT probe, the real‐time monitoring of drug‐induced hepatotoxicity was realized.

Anaerobic ammonium oxidation (anammox) was discovered as a new microbial reaction in the late 1990s, which led to the development of an innovative energy- and carbon-efficient technologypartial nitritation and anammox (PN/A)for nitrogen removal. PN/A was first applied to remove the nitrogen from high-strength wastewaters, e.g., anaerobic digestion liquor (i.e., sidestream), and further expanded to the main line of wastewater treatment plants (i.e., mainstream). While sidestream PN/A has been well-established with extensive full-scale installations worldwide, practical application of PN/A in mainstream treatment has been proven extremely challenging to date. A key challenge is achieving stable suppression of nitrite-oxidizing bacteria (NOB). This study examines the progress of NOB suppression in both sidestream- and mainstream PN/A over the past two decades. The successful NOB suppression in sidestream PN/A was reviewed, and these successes were evaluated in terms of their transferability into mainstream PN/A. Drawing on the learning over the past decades, we anticipate that a hybrid process, comprised of biofilm and floccular sludge, bears great potential to achieve efficient mainstream PN/A, while a combination of strategies is entailed for stable NOB suppression. Furthermore, the recent discovery of novel nitrifiers would trigger new opportunities and new challenges for mainstream PN/A.

Oxidation of ammonium to nitrite rather than nitrate, i.e., nitritation, is critical for autotrophic nitrogen removal. This study demonstrates a robust nitritation process in treating low-strength wastewater, obtained from a mixture of real mainstream sewage with sidestream anaerobic digestion liquor. This is achieved through cultivating acid-tolerant ammonia-oxidizing bacteria (AOB) in a laboratory nitrifying bioreactor at pH 4.5–5.0. It was shown that nitrite accumulation with a high NO2 –/(NO2 – + NO3 –) ratio of 95 ± 5% was stably maintained for more than 300 days, and the obtained volumetric NH4 + removal rate (i.e., 188 ± 14 mg N L–1 d–1) was practically useful. 16S rRNA gene sequencing analyses indicated the dominance of new AOB, “Candidatus Nitrosoglobus,” in the nitrifying guild (i.e., 1.90 ± 0.08% in the total community), with the disappearance of typical activated sludge nitrifying microorganisms, including Nitrosomonas, Nitrospira, and Nitrobacter. This is the first identification of Ca. Nitrosoglobus as key ammonia oxidizers in a wastewater treatment system. It was found that Ca. Nitrosoglobus can tolerate low pH (<5.0), and free nitrous acid (FNA) at levels that inhibit AOB and nitrite-oxidizing bacteria (NOB) commonly found in wastewater treatment processes. The in situ inhibition of NOB leads to accumulation of nitrite (NO2 –), which along with protons (H+) also produced in ammonium oxidation generates and sustains FNA at 3.0 ± 1.4 mg HNO2-N L–1. As such, robust PN was achieved under acidic conditions, with a complete absence of NOB. Compared to previous nitritation systems, this acidic nitritation process is featured by a higher nitric oxide (NO) but a lower nitrous oxide (N2O) emission level, with the emission factors estimated at 1.57 ± 0.08 and 0.57 ± 0.03%, respectively, of influent ammonium nitrogen load.