In Situ Investigation on the Effect of Salinity and pH on the Asphaltene Desorption under Flowing Conditions

There is a limited understanding of the microscale interactions between fluid–oil–solid interfaces, which could be a stumbling block to the development of relevant technologies and industries. With this in mind, we applied an in situ method, quartz crystal microbalance with dissipation (QCM-D), on the interactions among the fluid–oil–solid phases and investigated the desorption process of the asphaltene model molecule from silica surfaces during a flow of LSW at the conditions of different ion types, salinities, or pH values. The salinity effect plays a bigger role than that of the pH effect on the asphaltene desorption and, furthermore, the divalent ions (such as SO42–, Mg2+, or Ca2+) show a stronger effect than that of monovalent ions (such as Cl–, Na+, or K+). Our study provides a new strategy for the investigation of the interactions between fluid–oil–solid interfaces

Ultrasensitive Fluorometric Angling Determination of <i>Staphylococcus aureus</i> in Vitro and Fluorescence Imaging in Vivo Using Carbon Dots with Full-Color Emission

Rapid, accurate, and safe screening of foodborne pathogenic bacteria is essential to effectively control and prevent outbreaks of foodborne illness. Fluorescent sensors constructed from carbon dots (CDs) and nanomaterial-based quenchers have provided an innovative method for screening of pathogenic bacteria. Herein, an ultrasensitive magnetic fluorescence aptasensor was designed for separation and detection of Staphylococcus aureus (S. aureus). Multicolor fluorescent CDs with a long fluorescent lifetime (6.73 ns) and high fluorescence stability were synthesized using a facile hydrothermal approach and modified cDNA as a highly sensitive fluorescent probe. CD fluorescence was quenched by Fe3O4 + aptamer via fluorescence resonance energy transfer (FRET). Under optimal conditions, the FRET-based aptasensor can detect S. aureus accompanied by a wide linear range of 50–107 CFU·mL–1 and a detection limit of 8 CFU·mL–1. Compared with other standard methods, this method was faster and more convenient, and the entire test was finished within 30 min. The capability of the aptasensor was simultaneously investigated on food samples. Additionally, the developed CDs exhibited excellent biocompatibility and were thus applied as fluorescent probes for bioimaging both in vitro and in vivo. This new platform provided an excellent application of the CDs for detecting and bioimaging pathogenic bacteria

Desorption Mechanism of Asphaltenes in the Presence of Electrolyte and the Extended Derjaguin–Landau–Verwey–Overbeek Theory

Desorption of asphaltenes from silica-coated quartz crystals upon exposure to a series of saline solutions was studied through the measurements of quartz crystal microbalance with dissipation (QCM-D), atomic force microscopy (AFM), and contact angle. Interestingly, it was found that the mass loading and thickness of asphaltene film decreased during the injection of sodium chloride solution at the concentrations ranging from 1 to 10 mM, with the surface tending to be hydrophilic, whereas the mass loading and film thickness increased gradually when the concentration increased from 10 to 1000 mM, with the surface inclined to be hydrophobic. It was also found that the electrostatic force had a great effect on this process due to the interactions between the charged interfaces of oil/water and water/solid. Besides, some additional interactions may arise under small distance at the presence of the electrolyte solution, and therefore, a direct force-measuring technique was introduced, in which the functionalized AFM tips felt a solid surface to model the interactions among three phases of oil, water, and solid. Based on the computed results of disjoining pressure isotherms, the theory of Derjaguin–Landau–Verwey–Overbeek (DLVO) was extended, taking into account of the participation of hydration forces which played an important role at short range. These structural forces mostly originated from the overlap of the hydrated layers under a variety of salinity concentrations, resulting in the balance of resultant interactions