Comparison of the Antibacterial Activity of Selected Deep Eutectic Solvents (DESs) and Deep Eutectic Solvents Comprising Organic Acids (OA-DESs) Toward Gram-Positive and Gram-Negative Species.

Deep eutectic solvents (DESs) have been intensively investigated in recent years for their antibacterial properties, with DESs that comprise organic acids (OA-DESs) showing promising antibacterial action. However a majority of the reports focused only on a limited number strains and techniques, which is not enough to determine the antibacterial potential of a substance. To bridge this gap, the antibacterial activity of classical DESs and OA-DESs is assessed on twelve Gram-negative and Gram-positive bacteria strains, with some of them exhibiting specific resistance toward antibiotics. The investigated formulations of OA-DESs comprise glycolic, malic, malonic, and oxalic acids as representatives of this group. Using a range of microbiological assays as well as physicochemical characterization methods, a major difference of the effectiveness between the two groups is demonstrated, with OA-DESs exhibiting, as expected, greater antibacterial effectiveness than classical DESs. Most interestingly, slight differences in the minimum inhibitory and bactericidal concentration values as well as time-kill kinetics profiles are observed between Gram-positive and Gram-negative strains. Transmission electron microscopy analysis reveals the effect of the treatment of the bacteria with the representatives of both groups of DESs, which allows us to better understand the possible mechanism-of-action of these novel materials.

Deep Eutectic Solvents Comprising Organic Acids and Their Application in (Bio)Medicine.

Over the last years, we observed a significant increase in the number of published studies that focus on the synthesis and characterization of deep eutectic solvents (DESs). These materials are of particular interest mainly due to their physical and chemical stability, low vapor pressure, ease of synthesis, and the possibility of tailoring their properties through dilution or change of the ratio of parent substances (PS). DESs, considered as one of the greenest families of solvents, are used in many fields, such as organic synthesis, (bio)catalysis, electrochemistry, and (bio)medicine. DESs applications have already been reported in various review articles. However, these reports mainly described these components' basics and general properties without focusing on the particular, PS-wise, group of DESs. Many DESs investigated for potential (bio)medical applications comprise organic acids. However, due to the different aims of the reported studies, many of these substances have not yet been investigated thoroughly, which makes it challenging for the field to move forward. Herein, we propose distinguishing DESs comprising organic acids (OA-DESs) as a specific group derived from natural deep eutectic solvents (NADESs). This review aims to highlight and compare the applications of OA-DESs as antimicrobial agents and drug delivery enhancers-two essential fields in (bio)medical studies where DESs have already been implemented and proven their potential. From the survey of the literature data, it is evident that OA-DESs represent an excellent type of DESs for specific biomedical applications, owing to their negligible cytotoxicity, fulfilling the rules of green chemistry and being generally effective as drug delivery enhancers and antimicrobial agents. The main focus is on the most intriguing examples and (where possible) application-based comparison of particular groups of OA-DESs. This should highlight the importance of OA-DESs and give valuable clues on the direction the field can take.

An ultra-high bandwidth nano-electronic interface to the interior of living cells with integrated fluorescence readout of metabolic activity.

We present the first ever broadband, calibrated electrical connection to the inside of a cell. The interior of a vital, living cell contains multiple dynamic and electrically active organelles such as mitochondria, chloroplasts, lysosomes, and the endoplasmic reticulum. However, little is known about the detailed electrical activity inside the cell. Here we show an ultra-high bandwidth nano-electronic interface to the interior of living cells with integrated fluorescence readout of metabolic activity. On-chip/on-petri dish nanoscale capacitance calibration standards are used to quantify the electronic coupling from bench to cell from DC to 26 GHz (with cell images at 22 GHz). The interaction of static to high frequency electromagnetic fields with the cell constituents induce currents of free charges and local reorganization of linked charges. As such, this enables a direct, calibrated, quantitative, nanoscale electronic interface to the interior of living cells. The interface could have a variety of applications in interfacing life sciences to nano-electronics, including electronic assays of membrane potential dynamics, nano-electronic actuation of cellular activity, and tomographic, nano-radar imaging of the morphology of vital organelles in the cytoplasm, during all phases of the cell life cycle (from development to senescence), under a variety of physiological environments, and under a broad suite of pharmacological manipulations.

Cyclostationary-Based Vital Signs Detection Using Microwave Radar at 2.5 GHz.

Non-contact detection and estimation of vital signs such as respiratory and cardiac frequencies is a powerful tool for surveillance applications. In particular, the continuous wave bio-radar has been widely investigated to determine the physiological parameters in a non-contact manner. Since the RF-reflected signal from the human body is corrupted by noise and random body movements, traditional Fourier analysis fails to detect the heart and breathing frequencies. In this effort, cyclostationary analysis has been used to improve the radar performance for non-invasive measurement of respiratory rate and heart rate. However, the preliminary works focus only on one frequency and do not include the impact of attenuation and random movement of the body in the analysis. Hence in this paper, we evaluate the impact of distance and noise on the cyclic features of the reflected signal. Furthermore, we explore the assessment of second order cyclostationary signal processing performance by developing the cyclic mean, the conjugate cyclic autocorrelation and the cyclic cumulant. In addition, the analysis is carried out using a reduced number of samples to reduce the response time. Implementation of the cyclostationary technique using a bi-static radar configuration at 2.5 GHz is shown as an example to demonstrate the proposed approach.

Scanning Microwave Microscopy of Vital Mitochondria in Respiration Buffer.

We demonstrate imaging using scanning microwave microscopy (SMM) of vital mitochondria in respiration buffer. The mitochondria are isolated from cultured HeLa cells and tethered to a solid graphene support. The mitochondria are kept vital (alive) using a respiration buffer, which provides nutrients to sustain the Krebs cycle. We verify that the mitochondria are "alive" by measuring the membrane potential using a voltage sensitive fluorescent dye (TMRE). The organelles are measured capacitively at 7 GHz. Several technical advances are demonstrated which enable this work: 1) The SMM operates in an electrophysiologically relevant liquid (hence conducting) environment; 2) The SMM operates in tapping mode, averaging the microwave reflection measurement over many tapping periods; 3) A tuned reflectometer enables increased sensitivity; 4) Variable frequencies up to 18 GHz are used; 5) In contrast with traditional matching/resonant methods that exhibit high quality factor that fail in the presence of liquids, interferometric/tuned reflectometer gives the possibility to adjust the quality factor or sensitivity even in the presence of the liquid.