Herein we report a green method for the synthesis of organic-inorganic hybrid nanoflowers using a Trigonella foenum-graecum L. (TF) (Fenugreek seeds) extracts as an organic part and copper ions acting as an inorganic part. The organic-inorganic hybrid nanoflowers using TF seed extract (TF-Cu2+ hNFs) were characterized by SEM, XRD, EDX and FTIR. The morphology of the TF-Cu2+ hNFs was quite spherical and monodisperse with ∼18μm size. The TF-Cu2+ hNF exhibited the effective anti-bacterial activity against Enterococcus faecium, Enterococcus faecalis, Staphylococcus aureus, Bacillus cereus, Salmonella typhi and Escherichia coli at 1-10 µg ml-1 concentrations except against Pseudomonas aeruginosa and Haemophilus influenza. However, both TF-Cu2+ hNFs and free TF extracts showed any antifungal activities against Candida albicans or Candida glabrata. The study revealed that TF-Cu2+ hNFs could be used as a therapeutic agent for microbial infections and has the potential to overcome drug resistance.

Diagnosis of infection-causing microorganisms with sensitive, rapid, selective and economical diagnostic tests is critical to start the right treatment. With these tests, the spread of infections can be prevented. In addition to that, the detection of antimicrobial resistance also makes a significant contribution to public health. In recent years, different types of diagnostic tests have been developed as alternatives to traditional diagnostic tests used in clinics. In particular, colorimetric tests, which minimize the need for an instrument, have advantages owing to their cost effectiveness, rapid response and naked-eye detection and practical use. In this review, we especially focused on pH indicators and nanomaterial-based colorimetric tests in detection of infection-causing microorganisms and antimicrobial resistance.

The bacterial pathogens have caused various serious infectious diseases in the human body, and even some threats to human life by leading to deaths. Enterobacteriaceae species especially urease positive ones, Proteus mirabilis (P. mirabilis) and Klebsiella pneumoniae (K. pneumoniae), show resistance to antibiotics and cause respiratory and urinary tract infections. We have developed natural indicator-incorporated colorimetric urease tests with a naked eye and smartphone readout to rapidly, sensitively and economically detect P. mirabilis and K. pneumoniae. We utilized anthocyanin found as a predominant component in red cabbage (Brassica oleracea) extract as a natural pH indicator instead of toxic and synthetic indicators. As a mechanistic explanation for the detection of P. mirabilis and K. pneumoniae, urease enzymes secreted from the P. mirabilis and K. pneumoniae hydrolyze urea to produce ammonia (NH₃), which increases the pH value of the reaction environment and leads to deprotonation from anthocyanins. The changes in the molecular structure and electronic structure of anthocyanins are responsible for revealing many different colors. We demonstrated how some reaction parameters including the concentration of the bacteria (colony-forming unit, CFU), the concentration of anthocyanin in the tests, initial color and pH values (pHs) of the tests influence their detection performance. We further developed a 3D-printed smartphone platform with smartphone based digital image processing software to improve the detection limit and shorten the detection time. We claim that natural indicator-incorporated rapid urease tests providing colorimetric readout evaluated by the human eye and smartphone imaging processing has great potential in practical use and they can be implemented in clinics.