New synthetic routes were devised for total synthesis of Fe3+-bound (ferri-) salmycin B (Sal B) (1), glycan-based Sal analogues 2-5 and their Fe3+-unbound (desferri-) counterparts 1 '-5 ' for the structure to activity relationship (SAR) study. The results of SAR study reveal the effective structure of 1 and its desferri-counterpart 1 ' that are responsible for the observed inhibitory activity against Staphylococcus aureus (S. aureus). Among the analogues 2-5 and 2 '-5 ', glucose-based analogue 2 and its desferri-counterpart 2 ' exhibited inhibitory potency comparable to 1 and 1 '. Chemical modification of 2 ' for further antibacterial study enabled us to discover desferri-Sal analogue 7 ' that endowed with a simpler pharmacophore structure but significantly higher antibacterial potency against methicillin-sensitive and resistant S. aureus than the natural product 1 ' and even the clinical vancomycin. Together with a better hydrolytic stability and shorter synthetic route, the analogue 7 ' represents an attractive antibiotic lead for further exploration.

In this study, we demonstrated a facile method to fabricate ion sources using a laser printer for ambient ionization mass spectrometry (MS). Toner spots printed by a printer can readily facilitate ionizing volatile and semivolatile compounds derived from solid or liquid samples for MS analysis. The experimental arrangement involved positioning the toner-printed paper near the inlet of a mass spectrometer, which was subjected to a high electric potential (e.g., -6 kV). Volatile or semivolatile compounds deriving from the sample positioned below the metal inlet of the mass spectrometer were promptly ionized upon activating the mass spectrometer. No direct electrical connection or voltage application was required on the paper substrate. An electric field was established between the toner spot on the paper and the inlet applied with a high voltage to induce the dielectric breakdown of the surrounding air and water molecules. Consequently, ionic species, including electrons and cationic radicals, were generated. Subsequent ion-molecule reactions facilitated the production of protons for ionizing analytes present in the gas phase proximal to the inlet of the mass spectrometer. Deprotonated analytes were detected in the resultant mass spectra when employing the method in negative ion mode. This methodology presents a straightforward approach for analyzing analytes in the gas phase under ambient conditions utilizing an exceptionally uncomplicated experimental setup. In addition, the developed method can be used to detect trace 2,4-dinitrophenol, an explosive, with a limit of detection as low as ∼30 pg.

Pathogenic bacteria cause the deaths of millions of people every year. With the development of antibiotics, hundreds and thousands of people's lives have been saved. Nevertheless, bacteria can develop resistance to antibiotics, rendering them insensitive to antibiotics over time. Peptides containing specific amino acids can be used as antibacterial agents; however, they can be easily degraded by proteases in vivo. To address these issues, branched peptide dendrimers are now being considered as good antibacterial agents due to their high efficacy, resistance to protease degradation, and low cytotoxicity. The ease with which peptide dendrimers can be synthesized and modified makes them accessible for use in various biological and nonbiological fields. That is, peptide dendrimers hold a promising future as antibacterial agents with prolonged efficacy without bacterial resistance development. Their in vivo stability and multivalence allow them to effectively target multi-drug-resistant strains and prevent biofilm formation. Thus, it is interesting to have an overview of the development and applications of peptide dendrimers in antibacterial research, including the possibility of employing machine learning approaches for the design of AMPs and dendrimers. This review summarizes the synthesis and applications of peptide dendrimers as antibacterial agents. The challenges and perspectives of using peptide dendrimers as the antibacterial agents are also discussed.

Pathogenic bacteria, including drug-resistant variants such as methicillin-resistant Staphylococcus aureus (MRSA), can cause severe infections in the human body. Early detection of MRSA is essential for clinical diagnosis and proper treatment, considering the distinct therapeutic strategies for methicillin-sensitive S. aureus (MSSA) and MRSA infections. However, the similarities between MRSA and MSSA properties present a challenge in promptly and accurately distinguishing between them. This work introduces an approach to differentiate MRSA from MSSA utilizing matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) in conjunction with a neural network-based classification model. Four distinct strains of S. aureus were utilized, comprising three MSSA strains and one MRSA strain. The classification accuracy of our model ranges from 92 to 97

Europium ions (Eu3+) have been utilized as a fluorescence-sensing probe for a variety of analytes, including tetracycline (TC). When Eu3+ is chelated with TC, its fluorescence can be greatly enhanced. Moreover, Eu3+ possesses 6 unpaired electrons in its f orbital, which makes it paramagnetic. Being a hard acid, Eu3+ can chelate with hard bases, such as oxygen-containing functional groups (e.g., phosphates and carboxylates), present on the cell surface of pathogenic bacteria. Due to these properties, in this study, Eu3+ was explored as a magnetic-trapping and sensing probe against pathogenic bacteria present in complex samples. Eu3+ was used as a magnetic probe to trap bacteria such as Staphylococcus aureus, Escherichia coli, Enterococcus faecalis, Acinetobacter baumannii, Bacillus cereus, and Pseudomonas aeruginosa. The addition of TC facilitated the easy detection of magnetic Eu3+-bacterium conjugates through fluorescence spectroscopy, with a detection limit of approximately similar to 10(4) CFU mL(-1). Additionally, matrix-assisted laser desorption/ionization mass spectrometry was employed to differentiate bacteria tapped by our magnetic probes.

Coffee is a daily essential, with prices varying based on taste, aroma, and chemical composition. However, distinguishing between different coffee beans is challenging due to time-consuming and destructive sample pretreatment. This study presents a novel approach for directly analyzing single coffee beans through mass spectrometry (MS) without the need for sample pretreatment. Using a single coffee bean deposited with a solvent droplet containing methanol and deionized water, we generated electrospray to extract the main species for MS analysis. Mass spectra of single coffee beans were obtained in just a few seconds. To showcase the effectiveness of the developed method, we used palm civet coffee beans (kopi luwak), one of the most expensive coffee types, as model samples. Our approach distinguished palm civet coffee beans from regular ones with high accuracy, sensitivity, and selectivity. Moreover, we employed a machine learning strategy to rapidly classify coffee beans based on their mass spectra, achieving 99.58% accuracy, 98.75% sensitivity, and 100% selectivity in cross-validation. Our study highlights the potential of combining the single-bean MS method with machine learning for the rapid and non-destructive classification of coffee beans. This approach can help to detect low-priced coffee beans mixed with high-priced ones, benefiting both consumers and the coffee industry.

Phosphates play an essential role in our living systems. Therefore, it is important to have simple and effective methods to detect and monitor the level of phosphates in complex samples. In this study, a facile switch-on fluorescence sensing method is developed for the detection of phosphates. The sensing probes are composed of Gd3+ and riboflavin-5 '-phosphate (RFMP), which are hard acid and hard base, respectively. Gd3+ and RFMP can strongly bind via chelation once mixed. RFMP emits bright green fluorescence under ultraviolet (UV) light illumination. However, its fluorescence is quenched in the presence of Gd3+, presumably due to aggregation caused quenching. In the presence of phosphates, the fluorescence derived from RFMP on the Gd3+-RFMP can be restored owing to the competitive binding of phosphates with Gd3+ on the Gd3+-RFMP conjugates to release RFMP. In this study, we demonstrate the feasibility of using the developed sensing method to determine the level of phosphates from real world samples such as drinking water and fetal bovine serum under the illumination of a UV lamp (lambda max = 365 nm) simply with the naked eye. The lowest distinguishable concentration of using our detection method towards adenosine triphosphate and pyrophosphate with the naked eye is-1 mu M. Further-more, when fluorescence spectroscopy is used as a detection tool, the limit of detection has further reduced to-611 nM. The feasibility of using the developed sensing probes combined with fluorescence spectroscopy for quantitative analysis of phosphates in real samples is also demonstrated in this study.

Dyes have been widely used in various industries for coloring different materials. The discharge of dyes into wastewater remains an issue due to its polluting effect on the environment. Therefore, it is important to develop methods to effectively remove dyes from wastewater. In this study, we explore a new and facile method that can be used to rapidly remove dyes, i.e., methylene blue (MB) and methyl orange (MO), from aqueous solutions simply by using magnetic metal ions, (i.e., Gd3+ and Fe3+) as probes. We impose magnetism on anionic surfactants such as sodium dodecyl sulfate (SDS) when their concentrations reach a certain level (e.g., their critical micelle concentrations (CMC)), by attaching magnetic metal ions via electrostatic interactions. The generated magnetic Gd3+-SDS conjugates possess manipulable magnetism and can be simply isolated by applying an external magnet. The trapping capacities of our Gd3+-SDS probes against MB and MO are similar to 425 and similar to 25 mu mol g(-1), respectively. The dissociation constants of our probes toward MB and MO are 9.63 x 10(-6) and 2.42 x 10(-5), respectively. Dishwashing detergent solutions spiked with MB and MO are also used as the real samples to demonstrate the feasibility of using Gd3+ and Fe3+ as probes for real-world applications.

Triazine herbicides are commonly used in agriculture to eliminate weeds. However, they can persist in the environment. In this study, we explored a new method for detecting triazine herbicides in aqueous samples. We selected two triazine herbicides, namely, prometryn and ametryn, as model herbicides. To generate magnetic probes, we mixed aqueous Gd3+ with aqueous sodium dodecyl sulfate (SDS), which created magnetic probes made of Gd3+-SDS micelles. These probes showed a trapping capacity for the model herbicides. Results indicated that the trapping capacities of our magnetic probes for ametryn and prometryn were approximately 466 and 468 nmol mg−1, respectively. The dissociation constants of our probes toward ametryn and prometryn were 2.92 × 10−5 and 1.27 × 10−5, respectively. This is the first report that the developed magnetic probes can be used to trap triazine herbicides. For detection, we used carbon fiber ionization mass spectrometry (CFI-MS), which can be used to directly detect semi-volatiles from the samples in the condensed phase. Because of the semi-volatility of triazine herbicides, the herbicides trapped by the magnetic probes can be directly analyzed by CFI-MS without any elution steps. In addition, we also demonstrated the feasibility of using our approach for detecting triazine herbicides in lake water and drinking water.

Tetracycline (TC) is a broad-spectrum antibiotic and has been added to animal feeds to grow livestock under healthy conditions, making it important to have effective methods for rapidly detecting TC in complex samples. In this study, a novel method that uses lanthanide ions (i.e. Eu3+ and Gd3+) as magnetic and sensing probes for the detection of TC from aqueous samples is explored. When dissolving Gd3+ in tris(hydroxymethyl)aminomethane (Tris) buffer at pH 9, magnetic Gd3+-Tris conjugates can be readily generated. The magnetic Gd3+-Tris conjugates possess trapping capacity toward TC from sample solutions via the chelation of Gd3+ and TC. Eu3+ is used as the fluorescence sensing probe against TC on the Gd3+-TC conjugates via the antenna effect. The fluorescence response derived from Eu3+ is increased with the increase of TC trapped on the Gd3+-based probes. The linear dynamic range against TC ranges from 20 to 320 nM, whereas the limit of detection toward TC is ~2 nM. Furthermore, the developed sensing method can be employed for the visual assay of TC with a concentration above ~0.16 μM under UV light illumination in the dark. Furthermore, we have demonstrated the applicability of the developed method to quantify TC in a chicken broth sample with complex matrix. Our developed method offers several advantages, including high sensitivity and good selectivity, for the detection of TC in complex samples.

Tetracycline (TC) is an antibiotic that has been widely used in the animal husbandry. Thus, TC residues may be found in animal products. Developing simple and sensitive methods for rapid screening of TC in complex samples is of great importance. Herein, we demonstrate a fluorescence-sensing method using Zn2+ as sensing probes for the detection of TC. Although TC can emit fluorescence under the excitation of ultraviolet light, its fluorescence is weak because of dynamic intramolecular rotations, leading to the dissipation of excitation energy. With the addition of Zn2+ prepared in tris(hydroxymethyl)amino-methane (Tris), TC can coordinate with Zn2+ in the Zn2+-Tris conjugates to form Tris-Zn2+-TC complexes. Therefore, the intramolecular motions of TC are restricted to reduce nonradiative decay, resulting in the enhancement of TC fluorescence. Aggregation-induced emission effects also play a role in the enhancement of TC fluorescence. Our results show that the linear dynamic range for the detection of TC is 15–300 nM. Moreover, the limit of detection was ~7 nM. The feasibility of using the developed method for determination of the concentration of TC in a complex chicken broth sample is also demonstrated in this work.

This study demonstrated a facile ionization method with the use of real samples for the ionization of their main compositions at ambient conditions for mass spectrometric analysis. Analyte ions derived from the real samples were readily observed in the mass spectrum when placing the samples close (≤1 mm) to the inlet of the mass spectrometer applied with a high voltage. No additional accessories such as an ionization emitter, a plasma generator, or a high voltage power supply were required for this approach. Ionization of semivolatiles derived from the samples occurred between the samples and the inlet of the mass spectrometer presumably owing to the dielectric breakdown induced by the electric field provided by the mass spectrometer. Real samples including plants, medicine tablets, and gloves with contaminants were used as the model samples. The putative ionization mechanisms are also discussed in this study.

Escherichia coli are common pathogens, whereas E. coli O157:H7 is the most notorious E. coli strain, owing to its high virulence that can cause serious adverse effects and death. E. coli contains abundant peroxidases. Thus, the presence of E. coli can be determined by mixing E. coli with its substrate such as 3,5,3′,5′ tetramethylbenzidines (TMB) for endogenous peroxidase reactions. Under the presence of a high concentration of E. coli, colorless TMB turned to bluish, owing to the generation of the complexity of TMB and its oxidized TMB. To further reduce the detectable cell concentration, we developed an affinity-based method combined with an endogenous peroxidase reaction and mass spectrometric detection to detect E. coli. Affinity probes (diameter: ~20 µm) modified with maltose were generated for the enrichment of E. coli from sample solutions. E. coli trapped by the affinity probes was reacted with TMB in the presence of hydrogen peroxide for endogenous peroxidase reactions. Contactless atmospheric pressure ionization mass spectrometry was used for the detection of the reaction product, oxidized TMB (TMB cationic radical), to indicate the presence of target bacteria. The results showed that the developed method can be used to rapidly determine the presence of E. coli from a sample solution based on the detection of the TMB cationic radicals. The lowest detectable concentration of our method against E. coli O157:H7 in buffers and in complex juice samples was as low as ~100 cfu mL−1.

A sharp metal needle used as the ionization emitter in conventional atmospheric pressure chemical ionization (APCI) mass spectrometry (MS) is usually required for analyte ionization through corona discharge (i.e., gas discharge). Nevertheless, we herein demonstrate that an insulating fiber (tip diameter: 10–60 µm; length: ~ 1 cm) made of glass or bamboo can function as an APCI-like ionization emitter. Although no direct electric contact is made on the fiber, the ionization of volatiles and semi-volatiles occurs when the fiber is placed close (~ 1 mm) to the inlet of the mass spectrometer. No analyte ion signals can be observed without placing the insulating fiber in front of the mass spectrometer. The generation of ion species mainly relies on the electric field provided by the mass spectrometer. Presumably, owing to the high electric field provided by the mass spectrometer, the dielectric breakdown voltages of gas molecules in the air and the fiber are overcome, leading to the ionization of analytes in gas phase. In addition, the insulating fiber can function as a holder for sample solutions. Electrospray ionization–like processes derived from polar analytes such as amino acids, peptides, and proteins can readily occur when the insulating fiber deposited with a sample droplet is placed close to the inlet of the mass spectrometer. The feasibility of using the current approach for the detection of nonpolar and polar analytes from complex fetal bovine serum samples without tedious sample pretreatment is demonstrated in this work. The main advantage of using the suggested fiber is that the fiber can be used as the sampling probe to pick up samples and placed in front of a mass spectrometer for direct MS analysis. The application of using a robust, insulating, and disposable probe to pick up samples from real samples such as onion, honey, and pork samples followed by direct MS analysis is also demonstrated.

Aflatoxin B1 (AFB1) is a common mycotoxin present in agricultural and food products. Therefore, rapid screening methods must be developed for AFB1 detection with high sensitivity and good selectivity. In this study, we developed an analytical method based on the combination of solid-phase microextraction (SPME) with carbon fiber ionization (CFI)-mass spectrometry (MS) to detect the presence of trace AFB1 from complex samples. A pencil lead (type 2B, length: ~2.5 cm) with a sharp end (diameter: ~150 μm) was used as the SPME fiber and the ionization emitter in CFI-MS analysis. Owing to the graphite structure of the pencil lead, AFB1 can be trapped on the pencil lead through π–π interactions. After adsorbing AFB1, the pencil lead was directly introduced in a pipette tip (length: ~0.7 cm; tip inner diameter: ~0.6 mm), placed close (~1 mm) to the inlet of the mass spectrometer, and applied with a high voltage (−4.5 kV) for in situ AFB1 elution and CFI-MS analysis. A direct electric contact on the SPME-CFI setup was not required. Followed by the introduction of an elution solvent (10 μL) (acetonitrile/ethanol/deionized water, 2:2:1 (v/v/v)) to the pipette tip, electrospray ionization was generated from the elution solvent containing AFB1 for CFI-MS analysis. A reactive SPME-CFI-MS strategy was employed to further identify AFB1 and improve elution capacity using our approach. Butylamine was added to the elution solvent, which was then introduced to the pipette tip inserted with the SPME fiber. Butylamine-derivatized AFB1 was readily generated and appeared in the resultant SPME-CFI mass spectrum. The lowest detectable concentration against AFB1 using our approach was ~1.25 nM. Our method can distinguish AFB1 from AFG1 in a mixture and can be used for the detection of trace AFB1 in complex peanut extract samples.

Aflatoxin B1 (AFB1), commonly found in agriculture products, has been considered as a carcinogen. Thus, to develop analytical methods that can be used to rapidly screen the presence of AFB1 in complex samples is important. Surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) uses inorganic materials as assisting materials to facilitate desorption/ionization of analytes. The feasibility of using GO as the affinity probe against AFB1 and as the assisting material in SALDI-MS analysis was first demonstrated. We also explored a facile method to impose magnetism on GO to generate magnetic GO (MGO) nanoprobes by simply incubating GO in aqueous FeCl3 under microwave heating. The generated MGO nanoprobes possessed magnetism and were capable of enriching trace AFB1 from complex samples. AFB1 enrichment took only 6 min by incubating MGO with samples under microwave heating (power = 90 W). Followed by magnetic isolation, the isolated conjugates were ready for SALDI-MS analysis. The enrichment steps including trapping and isolation can be completed within ∼10 min. The lowest detectable concentration of our method toward AFB1 was ∼1 nM. Results also showed that AFB1 can be selectively detected from complex samples, including cell lysates of fungal spores, AFB1-spiked peanut, and wheat samples, by using the developed method. The selectivity of our method against AFB1 from the samples containing other toxins including aflatoxin G1 and ochratoxin A was also examined. According to these results, we believe that the developed method should have the potential to be used for rapid screening of AFB1 from real-world samples.

Capillary electrophoresis (CE) is an effective technique for the separation of different analytes. Moreover, online preconcentration of trace analytes in the capillary for CE analysis has been demonstrated. CE and capillary electrochromatography (CEC) are suitable for the separation of analytes with similar polarities. Given that CE and CEC are only used to separate small-volume samples, sensitive mass spectrometry (MS) is a suitable detection tool for CE and CEC. Contactless atmospheric pressure ionization (C-API) is a continuous flow ion source that only uses a short capillary as the ionization emitter operated at atmospheric pressure for MS analysis. In this study, we demonstrated the feasibility of hyphenating CE/CEC with C-API-MS by using a short and tapered capillary as the interface. The short capillary (a few centimeters) can function as the separation/preconcentration tube and the ionization emitter. This hyphenated technique can be used to analyze small organics within a few minutes. The suitability of using the hyphenated technique for online preconcentration, separation, and quantitative analysis for small organics is demonstrated in this study.

Escherichia coli O157:H7 and Staphylococcus aureus are common pathogens. Gram-negative bacteria, such as E. coli, contain high concentrations of endogenous peroxidases, whereas Gram-positive bacteria, such as S. aureus, possess abundant endogenous catalases. Colorless 3,5,3′,5′-tetramethyl benzidine (TMB) changes to blue oxidized TMB in the presence of E. coli and a low concentration of H2O2 (e.g., ~11 mM) at pH of 3. Moreover, visible air bubbles containing oxygen are generated after S. aureus reacts with H2O2 at a high concentration (e.g., 180 mM) at pH of 3. A novel method for rapidly detecting the presence of bacteria on the surfaces of samples, on the basis of these two endogenous enzymatic reactions, was explored. Briefly, a cotton swab was used for collecting bacteria from the surfaces of samples, such as tomatoes and door handles, then two-step endogenous enzymatic reactions were carried out. In the first step, a cotton swab containing bacteria was immersed in a reagent comprising H2O2 (11.2 mM) and TMB for 25 min. In the second step, the swab was dipped further in H2O2 (180 mM) at pH 3 for 5 min. Results showed that the presence of Gram-negative bacteria, such as E. coli with a cell number of ≥ ~105, and Gram-positive bacteria, such as S. aureus with a cell number of ≥ ~106, can be visually confirmed according to the appearance of the blue color in the swab and the formation of air bubbles in the reagent solution, respectively, within ~30 min. To improve visual sensitivity, we dipped the swab carrying the bacteria in a vial containing a growth broth, incubated it for ~4 h, and carried out the two-stage reaction steps. Results showed that bluish swabs resulting from the presence of E. coli O157: H7 with initial cell numbers of ≥ ~34 were obtained, whereas air bubbles were visible in the samples containing S. aureus with initial cell numbers of ≥ ~8.5 × 103.

Atmospheric pressure chemical ionization (APCI)-mass spectrometry (MS) and electrospray ionization (ESI)-MS can cover the analysis of analytes from low to high polarities. Thus, an ion source that possesses these two ionization functions is useful. Atmospheric surface-assisted ionization (ASAI), which can be used to ionize polar and nonpolar analytes in vapor, liquid, and solid forms, was demonstrated in this study. The ionization of analytes through APCI or ESI was induced from the surface of a metal substrate such as a titanium slab. ASAI is a contactless approach operated at atmospheric pressure. No electric contacts nor any voltages were required to be applied on the metal substrate during ionization. When placing samples with high vapor pressure in condensed phase underneath a titanium slab close to the inlet of the mass spectrometer, analytes can be readily ionized and detected by the mass spectrometer. Furthermore, a sample droplet (~2 μL) containing high-polarity analytes, including polar organics and biomolecules, was ionized using the titanium slab. One titanium slab is sufficient to induce the ionization of analytes occurring in front of a mass spectrometer applied with a high voltage. Moreover, this ionization method can be used to detect high volatile or polar analytes through APCI-like or ESI-like processes, respectively.

Magnetic trapping has been employed in the development of analytical methods owing to its ease and simplicity in handling samples. Nevertheless, the generation of functional probes is usually time consuming. A new and simple affinity method that uses gadolinium ion (Gd3+), a magnetic ion, as affinity probe for magnetic tapping of pathogenic bacteria was demonstrated in the present study. Escherichia coli O157:H7, Staphylococcus aureus, and Acinetobacter baumannii were selected as model bacteria. The model bacteria were magnetically isolated after incubation in Tris buffer (pH 8) containing Gd3+ (0.1 M) under microwave heating (power: 180 W, 90 s × 3). The resultant Gd3+-bacterium conjugates possessed sufficient magnetism, resulting in magnetic aggregations by an external magnet (∼4,000 Gauss). For ease of magnetic isolation, the sample containing Gd3+-bacterium complexes was stirred by a small magnet. After 1 h, the magnet attached with precipitates, i.e., Gd3+-bacterium conjugates, was readily removed using a pair of tweezers. The bacteria in the resultant conjugates were characterized by matrix-assisted laser desorption/ionization mass spectrometry. The limits of detection of the current approach toward E. coli O157:H7, S. aureus, and A. baumannii in complex samples were ∼104-105 cells mL-1.