Rapid estimation of bacteria by a fluorescent gold nanoparticle-polythiophene composite

Progress and challenges in bacterial infection theranostics based on functional metal nanoparticles

The rapid proliferation and infection of bacteria, especially multidrug-resistant bacteria, have become a great threat to global public health. Focusing on the emergence of "super drug-resistant bacteria" caused by the abuse of antibiotics and the insufficient and delayed early diagnosis of bacterial diseases, it is of great research significance to develop new technologies and methods for early targeted detection and treatment of bacterial infection. The exceptional effects of metal nanoparticles based on their unique physical and chemical properties make such systems ideal for the detection and treatment of bacterial infection both in vitro and in vivo. Metal nanoparticles also have admirable clinical application prospects due to their broad antibacterial spectrum, various antibacterial mechanisms and excellent biocompatibility. Herein, we summarized the research progress concerning the mechanism of metal nanoparticles in terms of antibacterial activity together with the detection of bacterial. Representative achievements are selected to illustrate the proof-of-concept in vitro and in vivo applications. Based on these observations, we also give a brief discussion on the current problems and perspective outlook of metal nanoparticles in the diagnosis and treatment of bacterial infection.

Antimicrobial Activity of Cationic Poly(3-hexylthiophene) Nanoparticles Coupled with Dual Fluorescent and Electrochemical Sensing: Theragnostic Prospect

Designing therapeutic and sensor materials to diagnose and eliminate bacterial infections remains a significant challenge for active theragnostic nanoprobes. In the present work, fluorescent/electroactive poly(3-hexylthiophene) P3HT nanoparticles (NPs) stabilized with quaternary ammonium salts using cetyltrimethylammonium bromide (CTAB), (CTAB-P3HT NPs) were prepared using a simple mini-emulsion method. The morphology, spectroscopic properties and electronic properties of CTAB-P3HT NPs were characterized by DLS, zeta potential, SEM, TEM, UV-vis spectrophotometry, fluorescence spectroscopy and electrochemical impedance spectroscopy (EIS). In an aqueous solution, CTAB-P3HT NPs were revealed to be uniformly sized, highly fluorescent and present a highly positively charged NP surface with good electroactivity. Dual detection was demonstrated as the binding of the bacteria to NPs could be observed by fluorescence quenching as well as by the changes in EIS. Binding of E. coli to CTAB-P3HT NPs was demonstrated and LODs of 5 CFU/mL and 250 CFU/mL were obtained by relying on the fluorescence spectroscopy and EIS, respectively. The antimicrobial activity of CTAB-P3HT NPs on bacteria and fungi was also studied under dark and nutritive conditions. An MIC and an MBC of 2.5 µg/mL were obtained with E. coli and with S. aureus, and of 0.312 µg/mL with C. albicans. Additionally a good biocompatibility toward normal human cells (WI38) was observed, which opens the way to their possible use as a therapeutic agent.

Nano-enabled sensing approaches for pathogenic bacterial detection

Infectious diseases caused by pathogenic bacteria, especially antibiotic-resistant bacteria, are one of the biggest threats to global health. To date, bacterial contamination is detected using conventional culturing techniques, which are highly dependent on expert users, limited by the processing time and on-site availability. Hence, real-time and continuous monitoring of pathogen levels is required to obtain valuable information that could assist health agencies in guiding prevention and containment of pathogen-related outbreaks. Nanotechnology-based smart sensors are opening new avenues for early and rapid detection of such pathogens at the patient's point-of-care. Nanomaterials can play an essential role in bacterial sensing owing to their unique optical, magnetic, and electrical properties. Carbon nanoparticles, metallic nanoparticles, metal oxide nanoparticles, and various types of nanocomposites are examples of smart nanomaterials that have drawn intense attention in the field of microbial detection. These approaches, together with the advent of modern technologies and coupled with machine learning and wireless communication, represent the future trend in the diagnosis of infectious diseases. This review provides an overview of the recent advancements in the successful harnessing of different nanoparticles for bacterial detection. In the beginning, we have introduced the fundamental concepts and mechanisms behind the design and strategies of the nanoparticles-based diagnostic platform. Representative research efforts are highlighted for in vitro and in vivo detection of bacteria. A comprehensive discussion is then presented to cover the most commonly adopted techniques for bacterial identification, including some seminal studies to detect bacteria at the single-cell level. Finally, we discuss the current challenges and a prospective outlook on the field, together with the recommended solutions.

Single-Cell Biodetection by Upconverting Microspinners

Near-infrared-light-mediated optical tweezing of individual upconverting particles has enabled all-optical single-cell studies, such as intracellular thermal sensing and minimally invasive cytoplasm investigations. Furthermore, the intrinsic optical birefringence of upconverting particles renders them light-driven luminescent spinners with a yet unexplored potential in biomedicine. In this work, the use of upconverting spinners is showcased for the accurate and specific detection of single-cell and single-bacteria attachment events, through real-time monitoring of the spinners rotation velocity of the spinner. The physical mechanisms linking single-attachment to the angular deceleration of upconverting spinners are discussed in detail. Concomitantly, the upconversion emission generated by the spinner is harnessed for simultaneous thermal sensing and thermal control during the attachment event. Results here included demonstrate the potential of upconverting particles for the development of fast, high-sensitivity, and cost-effective systems for single-cell biodetection.

Metal Nanoparticles for Diagnosis and Therapy of Bacterial Infection

Infectious diseases caused by pathogenic bacteria, especially multidrug-resistant bacteria, and their global spreading have become serious public health concerns. Early diagnosis and effective therapy can efficiently prevent deterioration and further spreading of the infections. There is an urgent need for sensitive, selective, and facile diagnosis as well as therapeutically potent treatment. The emergence of nanotechnology has provided more options for diagnosis and treatments of bacterial infections. Metal nanoparticles and metal oxide nanoparticles have drawn intense attention owing to their unique optical, magnetic, and electrical properties. These versatile metal-based nanoparticles have great potential for selective detection of bacteria and/or therapy. This review gives an overview of recent efforts on developing various metal-based nanoparticles for bacterial detection and infection therapy. It begins with an introduction of fundamental concepts and mechanisms in designing diagnostic and therapeutic strategies. Representative achievements are selected to illustrate the proof-of-concept in vitro and in vivo applications. A brief discussion of challenges and perspective outlook in this field is provided at the end of this review.

Selective Sensing and Imaging of Penicillium italicum Spores and Hyphae Using Carbohydrate-Lectin Interactions

The blue-green mold Penicillium italicum is among the most problematic post-harvest plant infections limiting the integrity of citrus and many other crops during storage and transportation, but there is no sensor for its on-site or field detection. We hereby, for the first time, report the development of novel biomolecular sensor for assessing the presence of P. italicum spores and hyphae using carbohydrate-lectin recognitions. Two approaches were developed: (i) lateral tests using standalone poly(amic) acid (PAA) membranes and glass surfaces and (ii) quantitative tests on 96-well polystyrene plates and paper electrodes. In both cases, the surfaces were functionalized with novel derivatized sugar based ligands while staining was performed with gold nanoparticles. Both approaches provided strong signals for 10⁴ spores/mL of P. italicum isolated from experimentally infected lemons as the lowest-reliable concentration. The 96-well plate-based gave the most sensitive detection with a 4 × 10² spores/mL limit of detection, a linear dynamic range between 2.9 × 10³ and 6.02 × 10⁴ spores/mL ( R² = 0.9939) and standard deviation of less than 5% for five replicate measurements. The selectivity of the ligands was tested against Trichaptum biforme, Glomerulla cingulata ( Colletotrichum gloeosporioides), and Aspergillus nidulans fungi species. The highest selectivity was obtained using the sugar-based gold-nanoparticles toward both the spores and the hyphae of P. italicum. The advanced specificity was provided by the utilized sugar ligands employed in the synthesis of gold nanoparticles and was independent from size and shapes of the AuNPs. Accuracy of the sensor response showed dramatic dependence on the sample preparation. In the case of 5-10 min centrifugation at 600 rpm, the spores can be isolated free from hyphae and conidiophore, for which spiked recovery was up to 95% (std ±4). In contrast, for gravity-based precipitation of hyphae, the spiked recovery was 88% (std 11).

Influence of Hofmeister I- on Tuning Optoelectronic Properties of Ampholytic Polythiophene by Varying pH and Conjugating with RNA

A significant tuning of optoelectronic properties of polythiophene (PT) chains due to Hofmeister iodide (I^-) ion is demonstrated in ampholytic polythiophene [polythiophene-g-poly{(N,N,N-trimethylamino iodide)ethyl methacrylate-co-methacrylic acid}, APT] at different pHs. In acidic medium, the absorption and emission signals of PT chromophore exhibit appreciable blue shift in the presence of I^- as counteranion only. The cooperative effect of undissociated -COOH and quaternary ammonium groups immobilize I^- near the apolar PT chain causing threading of grafted chains and hence twisting of the backbone attributing to the blue shift. As medium pH is increased, dethreading of the PT backbone occurs due to ionization of -COOH group, releasing quencher iodide ions from the vicinity of the PT chains resulting in a red shift in absorption and a sharp hike in fluorescence intensity (390 times) for an increase of excitons lifetime. With an increase of pH, morphology changes from a multivesicular aggregate with vacuoles to smaller size vesicles and finally to nanofibrillar network structure. Dethreading is also found when APT interacts with RNA showing a significant hike of fluorescence (22 times) for displacing iodide ions forming a nanofibrillar network morphology. Threading and dethreading also affect the resistance, capacitance, and Warburg impedance values of APT. Molecular dynamics simulation of a model APT chain in a water box supports the threading at lower pH where the iodide ions pose nearer to the PT chain than that at higher pH causing dethreading. So the influence of Hofmeister I^- ion is established for tuning the optoelectronic properties of a novel PT based polyampholyte by changing pH or by conjugating with RNA.

Recent advances in M13 bacteriophage-based optical sensing applications

Recently, M13 bacteriophage has started to be widely used as a functional nanomaterial for various electrical, chemical, or optical applications, such as battery components, photovoltaic cells, sensors, and optics. In addition, the use of M13 bacteriophage has expanded into novel research, such as exciton transporting. In these applications, the versatility of M13 phage is a result of its nontoxic, self-assembling, and specific binding properties. For these reasons, M13 phage is the most powerful candidate as a receptor for transducing chemical or optical phenomena of various analytes into electrical or optical signal. In this review, we will overview the recent progress in optical sensing applications of M13 phage. The structural and functional characters of M13 phage will be described and the recent results in optical sensing application using fluorescence, surface plasmon resonance, Förster resonance energy transfer, and surface enhanced Raman scattering will be outlined.

Polythiophene biosensor for rapid detection of microbial particles in water

Most microbial particles have a negatively charged surface and in this work, we describe a water quality monitoring application of a cationic polythiophene derivative (AH-35) for the rapid assessment of microbial contamination of water. Using E. coli as a prototype microbial particle, we demonstrate that the AH-35 polymer can provide a qualitative assessment of water if exposed to more than 500 CFU/mL, thereby paving the way to a new family of biosensors potentially useful for monitoring drinking water distribution systems.

Membrane-directed high bactericidal activity of (gold nanoparticle)-polythiophene composite for niche applications against pathogenic bacteria

The use of nanoscale materials as bactericidal agents represents a novel paradigm in the development of therapeutics against drug-resistant pathogenic bacteria. In this paper the antimicrobial activity of a water soluble (gold nanoparticle)-polythiophene (AuNP-PTh) composite against common bacterial pathogens is reported. The nanocomposite is broad-spectrum in its bactericidal activity and exhibits a membrane-directed mode of action on target pathogens. The therapeutic potency of AuNP-PTh is demonstrated by experiments which reveal that the nanocomposite can breach the outer membrane defense barrier of Gram-negative pathogens for subsequent killing by a hydrophobic antibiotic, inhibit the growth of model gastrointestinal pathogens in simulated gastric fluid, and significantly eradicate bacterial biofilms. The high bacterial selectivity and lack of cytotoxicity on human cells augers well for future therapeutic application of the nanocomposite against clinically relevant pathogenic bacteria.

Quick and simple estimation of bacteria using a fluorescent paracetamol dimer-Au nanoparticle composite

Rapid, simple and sensitive detection of bacterial contamination is critical for safeguarding public health and the environment. Herein, we report an easy method of detection as well as enumeration of the bacterial cell number on the basis of fluorescence quenching of a non-antibacterial fluorescent nanocomposite, consisting of paracetamol dimer (PD) and Au nanoparticles (NPs), in the presence of bacteria. The composite was synthesized by reaction of paracetamol (p-hydroxyacetanilide) with HAuCl(4). The Au NPs of the composite were characterized using UV-Vis spectroscopy, transmission electron microscopy (TEM), X-ray diffraction and selected area electron diffraction analysis. The paracetamol dimer in the composite showed emission peak at 435 nm when excited at 320 nm. The method successfully detected six bacterial strains with a sensitivity of 100 CFU mL(-1). The gram-positive and gram-negative bacteria quenched the fluorescence of the composite differently, making it possible to distinguish between the two. The TEM analysis showed interaction of the composite with bacteria without any apparent damage to the bacteria. The chi-square test established the accuracy of the method. Quick, non-specific and highly sensitive detection of bacteria over a broad range of logarithmic dilutions within a short span of time demonstrates the potential of this method as an alternative to conventional methods.

Phenylboronic acid functionalized gold nanoparticles for highly sensitive detection of Staphylococcus aureus

Herein, we report a phenylboronic acid functionalized gold nanoparticle (GNP)-based colorimetric assay for rapid detection of Staphylococcus aureus (S. aureus) with high sensitivity. In this approach, GNPs can bind to S. aureus by the reaction of phenylboronic acid with the cis-diol configuration in glycans on the bacterial surface, providing a colorimetric readout of the binding event. Using this strategy, we have been able to quantify S. aureus at a concentration of 50 cells per mL (three times the standard deviation divided by the slope of the working curve) in aqueous solution.

Functionalized gold nanoparticle supported sensory mechanisms applied in detection of chemical and biological threat agents: a review

There is a great necessity for development of novel sensory concepts supportive of smart sensing capabilities in defense and homeland security applications for detection of chemical and biological threat agents. A smart sensor is a detection device that can exhibit important features such as speed, sensitivity, selectivity, portability, and more importantly, simplicity in identifying a target analyte. Emerging nanomaterial based sensors, particularly those developed by utilizing functionalized gold nanoparticles (GNPs) as a sensing component potentially offer many desirable features needed for threat agent detection. The sensitiveness of physical properties expressed by GNPs, e.g. color, surface plasmon resonance, electrical conductivity and binding affinity are significantly enhanced when they are subjected to functionalization with an appropriate metal, organic or biomolecular functional groups. This sensitive nature of functionalized GNPs can be potentially exploited in the design of threat agent detection devices with smart sensing capabilities. In the presence of a target analyte (i.e., a chemical or biological threat agent) a change proportional to concentration of the analyte is observed, which can be measured either by colorimetric, fluorimetric, electrochemical or spectroscopic means. This article provides a review of how functionally modified gold colloids are applied in the detection of a broad range of threat agents, including radioactive substances, explosive compounds, chemical warfare agents, biotoxins, and biothreat pathogens through any of the four sensory means mentioned previously.

RNA-poly(o-methoxyaniline) hybrid templated growth of silver nanoparticles and nanojacketing: physical and electronic properties

Three nanobiocomposites (PRAg31, PRAg11, and PRAg13; the numbers indicate the weight ratios of poly(o-methoxyaniline) (POMA) and ribonucleic acid (RNA), respectively), produced from the same amount of POMA (P) and silver nitrate (AgNO(3)) with differing proportions of RNA (R) are prepared by aging the aqueous solutions of the mixture for 3 weeks at 30 degrees C. The scanning and transmission electron microscopy (SEM and TEM) indicate Ag nanoparticle formation on the hybrid fiber surface and in the PRAg31 system the hybrid fibrils become coated with metallic Ag, the phenomenon being termed as "nanojacketting". The circular dichroism (CD) spectra indicate a small distortion of RNA conformation from A helix toward B helix. FTIR and UV-vis spectra suggest that POMA (emeraldine base, EB) being doped by Ag(+) become oxidized to its pernigraniline base (PB) form and reduce Ag(+) to metallic Ag. The Ag nanoparticles thus produced become stabilized on the fibril surface by co-ordination through nitrogen atoms of POMA (PB) chains. The much slower red shift of pi band to polaron band transition peak in PRAg31 than that of the other two nanobiocomposites is indicative of difficulty in conformational transitions of POMA chain in the "nanojacketted" hybrid fibrils. The dc-conductivity values of the nanobiocomposites are two orders higher than that of the pure POMA-RNA hybrids. The PRAg31 system exhibits rectification property in the I-V characteristic curves and a probable explanation based on the feasibility of p-n junction formation arising from the transfer of lone pair of electrons of nitrogen of POMA (p-type) to the Ag nanoparticles (n-type) has been offered.

Virus-based chemical and biological sensing

Viruses have recently proven useful for the detection of target analytes such as explosives, proteins, bacteria, viruses, spores, and toxins with high selectivity and sensitivity. Bacteriophages (often shortened to phages), viruses that specifically infect bacteria, are currently the most studied viruses, mainly because target-specific nonlytic phages (and the peptides and proteins carried by them) can be identified by using the well-established phage display technique, and lytic phages can specifically break bacteria to release cell-specific marker molecules such as enzymes that can be assayed. In addition, phages have good chemical and thermal stability, and can be conjugated with nanomaterials and immobilized on a transducer surface in an analytical device. This Review focuses on progress made in the use of phages in chemical and biological sensors in combination with traditional analytical techniques. Recent progress in the use of virus-nanomaterial composites and other viruses in sensing applications is also highlighted.