Gold nanoparticle-based optical nanosensors for food and health safety monitoring: recent advances and future perspectives

Modern society has been facing serious health-related problems including food safety, diseases and illness. Hence, it is urgent to develop analysis methods for the detection and control of food contaminants, disease biomarkers and pathogens. As the traditional instrumental methods have several disadvantages, including being time consuming, and having high cost and laborious procedures, optical nanosensors have emerged as promising alternative or complementary approaches to those traditional ones. With the advantages of simple preparation, high surface-to-volume ratio, excellent biocompatibility, and especially, unique optical properties, gold nanoparticles (AuNPs) have been demonstrated as excellent transducers for optical sensing systems. Herein, we provide an overview of the synthesis of AuNPs and their excellent optical properties that are ideal for the development of optical nanosensors based on local surface plasmon resonance (LSPR), colorimetry, fluorescence resonance energy transfer (FRET), and surface-enhanced Raman scattering (SERS) phenomena. We also review the sensing strategies and their mechanisms, as well as summarizing the recent advances in the monitoring of food contaminants, disease biomarkers and pathogens using developed AuNP-based optical nanosensors in the past seven years (2015–now). Furthermore, trends and challenges in the application of these nanosensors in the determination of those analytes are discussed to suggest possible directions for future developments.

We provide an overview of the synthesis of AuNPs and their excellent optical properties for the development of optical nanosensors including colorimetric, fluorescence resonance energy transfer, and surface-enhanced Raman scattering sensors.     

Management of COPD in Asia: A position statement of the Asian Pacific Society of Respirology

Chronic obstructive pulmonary disease (COPD) is a major disease in Asia. However, how to manage specifically Asian COPD patients has not been proposed. Awareness of COPD is very low and underdiagnosis/undertreatment is common in Asian countries. Low utilization of pulmonary function test and inhalers is also a problem. Moreover, high smoking prevalence and air pollution are barriers to managing Asian patients with COPD. The relatively low body mass index of Asian patients with COPD can increase their risk for experiencing adverse effects from COPD drugs. Physicians should consider the unique features of Asian populations with COPD such as the high prevalence rates of bronchiectasis and tuberculosis‐destroyed lungs, biomass smoke exposure and parasitic infection.     

Transvenous retrograde embolization of ruptured brain arteriovenous malformations: A case report and review of the literature

Hemorrhagic stroke due to ruptured brain arteriovenous malformations (AVMs) is a common cause in young stroke patients. When the ruptured AVMs are in deep location, the choice of endovascular intervention with the arterial approach to AVM embolization is routine but in many cases, it is not feasible due to the inability to access because of the small and tortuous arterial branch, however, the intravenous approach also results in high complete obliteration rates but also carries a higher risk of stroke than the intra-arterial route. We describe a 36-year-old female patient diagnosed with intracranial and intraventricular hemorrhage who underwent complete transvenous embolization of the ruptured AVMs, and achieved near-complete clinical recovery after 1 month with the modified Rankin scale 1.     

Primary intraventricular gliosarcoma on MRI: A challenging diagnosis

Gliosarcoma (GS) is an uncommon central nervous system tumor with several characteristics of a malignant neoplasm and poor prognosis. The majority of GS reports describe a predilection for the cerebral hemispheres, and cases of intraventricular GS are extremely rare, with only a few reported. In addition, intraventricular GS has not been associated with any unique radiographic or clinical features, which can result in misdiagnosis as other intraventricular tumor types. In this report, we present the case of a 32-year-old woman with GS in the trigone of the lateral ventricle and provide a retrospective review of similar, previously reported cases.     

High-speed atomic force microscopy reveals a three-state elevator mechanism in the citrate transporter CitS

The secondary active transporter CitS shuttles citrate across the cytoplasmic membrane of gram-negative bacteria by coupling substrate translocation to the transport of two Na⁺ ions. Static crystal structures suggest an elevator type of transport mechanism with two states: up and down. However, no dynamic measurements have been performed to substantiate this assumption. Here, we use high-speed atomic force microscopy for real-time visualization of the transport cycle at the level of single transporters. Unexpectedly, instead of a bimodal height distribution for the up and down states, the experiments reveal movements between three distinguishable states, with protrusions of ∼0.5 nm, ∼1.0 nm, and ∼1.6 nm above the membrane, respectively. Furthermore, the real-time measurements show that the individual protomers of the CitS dimer move up and down independently. A three-state elevator model of independently operating protomers resembles the mechanism proposed for the aspartate transporter Glt_Ph. Since CitS and Glt_Ph are structurally unrelated, we conclude that the three-state elevators have evolved independently.

The cytoplasmic membrane forms a semipermeable barrier between the cellular interior and the periplasm of bacteria. The trafficking of molecules across the membrane is necessary for the cell’s metabolism and is mediated by membrane transporters. These proteins are embedded in the lipid bilayer and undergo conformational changes leading to alternating exposure of the substrate-binding site to either side of the membrane. In secondary active transporters, the transitions between these conformational changes are strictly coupled to the binding and unbinding of not only the primary transported substrate but also a secondary substrate, which leads to their combined transport. Secondary substrates are usually protons or sodium ions of which membrane gradients are maintained in cells, which thereby provides the free energy gain necessary for substrate transport (1).The secondary active transporter CitS mediates the accumulation of citrate in gram-negative bacteria by mechanistic coupling of substrate translocation to the transport of two Na⁺ ions across the cytoplasmic membrane. In the pathogen Klebsiella pneumoniae, CitS is responsible for citrate uptake in the anaerobic citrate degradation pathway (2). CitS belongs to the 2-HydrocyCarboxylate Transporter family. Other members of this family are capable of transporting mono-, di-, and tricarboxylates containing a 2-hydroxy group. These proteins are involved in several energy conservation pathways such as citrate fermentation, malolactic fermentation, citrolactic fermentation, and oxidative malate decarboxylation (3–5). Crystal structures have been solved of CitS from K. pneumoniae and Salmonella enterica (6). The quaternary structure revealed that CitS is a homodimer, with each protomer consisting of two domains: a dimerization domain located centrally and a transport domain located peripherally (SI Appendix, Fig. S1). This dimeric structural arrangement of CitS leads to the presence of two identical transport routes per complex.Before the first structure of CitS was revealed, the alternating access was explained as a “rocker switch” mechanism similarly to LacY and GlpT, two transporters for which crystal structures were available at the time (7, 8). The publication of the structure of CitS from S. enterica suggested that the translocation of the substrates occurs by an elevator mechanism, similarly to the aspartate transporters Glt_Ph and Glt_Tk (9, 10). The structure of CitS suggests that the dimerization domains serve as central membrane anchor, and the peripheral transport domains can move up and down through the bilayer during turnover as a rigid body. This movement leads to a displacement of the binding site by 17 Å perpendicular to the membrane plane, as well as a rotation by ∼35°, and shuttles the protein between the outward-facing and inward-facing conformations (11). This elevator-type mechanistic interpretation, however, was inferred solely from the static crystal structures, and dynamic experiments have not been reported to test this assumption. In this respect, high-speed atomic force microscopy (HS-AFM) (12–15) offers the advantage of probing membrane proteins in liquid in their lipidic environment with high spatial and temporal resolution (16, 17). Uptake experiments performed on CitS report an apparent turnover rate of roughly once every second at saturating conditions (SI Appendix, Table S1) (18). This rate is within the scanning capabilities of HS-AFM, and here, we report HS-AFM experiments directly visualizing the dynamics of citrate transport, at the single-molecule level, to unveil the molecular mechanism behind transport.     

Chemical synthesis of Nd2Fe14B/Fe–Co nanocomposite with high magnetic energy product

Nd₂Fe₁₄B is one of the most popular permanent magnets (PMs) possessing the best energy product (BH)_max among the common PM materials. However, exchange-coupled nanocomposite magnets fabricated by embedding nanostructures of soft-phase magnetic materials into a hard-phase magnetic matrix manifest higher remanence and a higher energy product. Here we present the fabrication of exchange coupled Nd₂Fe₁₄B/Fe–Co magnetic nanocomposites using gel-combustion and diffusion–reduction processes. Pre-fabricated CoFe₂O₄ nanoparticles (NPs) of ∼5 nm diameter were incorporated into a Nd–Fe–B oxide matrix during its synthesis by gel-combustion. The obtained mixed oxide was further processed with oxidative annealing at 800 °C for 2 h and reductive annealing at 900 °C for 2 h to form a Nd₂Fe₁₄B/Fe–Co nanocomposite. Nanocomposites with different mol% of soft-phase were prepared and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and physical property measurement system (PPMS) to study their crystalline phase, morphology and magnetic behavior. Addition of 7.7 mol% of soft-phase was found to be optimum, producing a coercivity (H_c) of 5.6 kOe and remanence (M_r) of 54 emu g⁻¹ in the nanocomposite.

Nd₂Fe₁₄B is one of the most popular permanent magnets (PMs) possessing the best energy product (BH)_max among the common PM materials.     

Antioxidant and UV-radiation absorption activity of aaptamine derivatives – potential application for natural organic sunscreens

Antioxidant and UV absorption activities of three aaptamine derivatives including piperidine[3,2-b]demethyl(oxy)aaptamine (C1), 9-amino-2-ethoxy-8-methoxy-3H-benzo[de][1,6]naphthyridine-3-one (C2), and 2-(sec-butyl)-7,8-dimethoxybenzo[de]imidazo[4,5,1-ij][1,6]-naphthyridin-10(9H)-one (C3) were theoretically studied by density functional theory (DFT). Direct antioxidant activities of C1–C3 were firstly evaluated via their intrinsic thermochemical properties and the radical scavenging activity of the potential antioxidants with the HOO˙/HO˙ radicals via four mechanisms, including: hydrogen atom transfer (HAT), single electron transfer (SET), proton loss (PL) and radical adduct formation (RAF). Kinetic calculation reveals that HOO˙ scavenging in water occurs via HAT mechanism with C1 (k_app, 7.13 × 10⁶ M⁻¹ s⁻¹) while RAF is more dominant with C2 (k_app, 1.40 × 10⁵ M⁻¹ s⁻¹) and C3 (k_app, 2.90 × 10⁵ M⁻¹ s⁻¹). Antioxidant activity of aaptamine derivatives can be classified as C1 > C3 > C2. Indirect antioxidant properties based on Cu(i) and Cu(ii) ions chelating activity were also investigated in aqueous phase. All three studied compounds show spontaneous and favorable Cu(i) ion chelating activity with ΔG⁰ being −15.4, −13.7, and −15.7 kcal mol⁻¹, whereas ΔG⁰ for Cu(ii) chelation are −10.4, −10.8, and −2.2 kcal mol⁻¹ for C1, C2 and C3, respectively. In addition, all compounds show UVA and UVB absorption; in which the excitations are determined mostly as π–π* transition. Overall, the results suggest the potential applications of the aaptamines in pharmaceutics and cosmetics, i.e. as a sunscreen and antioxidant ingredient.

Antioxidant and UV absorption activities of three aaptamine derivatives were theoretically studied by density functional theory (DFT) and time-dependent density functional theory (TD-DFT).     

Enhancing the chloramphenicol sensing performance of Cu–MoS2 nanocomposite-based electrochemical nanosensors: roles of phase composition and copper loading amount

The rational design of nanomaterials for electrochemical nanosensors from the perspective of structure–property–performance relationships is a key factor in improving the analytical performance toward residual antibiotics in food. We have investigated the effects of the crystalline phase and copper loading amount on the detection performance of Cu–MoS₂ nanocomposite-based electrochemical sensors for the antibiotic chloramphenicol (CAP). The phase composition and copper loading amount on the MoS₂ nanosheets can be controlled using a facile electrochemical method. Cu and Cu₂O nanoparticle-based electrochemical sensors showed a higher CAP electrochemical sensing performance as compared to CuO nanoparticles due to their higher electrocatalytic activity and conductivity. Moreover, the design of Cu–MoS₂ nanocomposites with appropriate copper loading amounts could significantly improve their electrochemical responses for CAP. Under optimized conditions, Cu–MoS₂ nanocomposite-based electrochemical nanosensor showed a remarkable sensing performance for CAP with an electrochemical sensitivity of 1.74 μA μM⁻¹ cm⁻² and a detection limit of 0.19 μM in the detection range from 0.5–50 μM. These findings provide deeper insight into the effects of nanoelectrode designs on the analytical performance of electrochemical nanosensors.

In this work, we clarify the roles of phase composition and copper loading amount on the CAP sensing performance of Cu–MoS₂ nanocomposite-based electrochemical nanosensors.