Highly sensitive bacterial susceptibility test against penicillin using parylene-matrix chip

A penicillinase-modified poly(N-isopropylacrylamide-co-acrylamide) smart hydrogel biosensor with superior recyclability for sensitive and colorimetric detection of penicillin G

Antibiotics are widely used for treating bacterial infections. However, excessive or improper use of antibiotics can pose a serious threat to human health and water environments, and thus, developing cost-effective, portable and effective strategies to analyze and detect antibiotics is highly desired. Herein, we reported a responsive photonic hydrogel (RPH)-based optical biosensor (PPNAH) with superior recyclability for sensitive and colorimetric determination of a typical β-lactam antibiotic penicillin G (PG) in water. This sensor was composed of poly(N-isopropylacrylamide-co-acrylamide) smart hydrogel with incorporated penicillinase and Fe3O4@SiO2 colloidal photonic crystals (CPCs). The sensor could translate PG concentration signals into changes in the diffraction wavelength and structural color of the hydrogel. It possessed high sensitivity and selectivity to PG and excellent detection performances for other two typical β-lactam antibiotics. Most importantly, due to the unique thermosensitivity of the poly(N-isopropylacrylamide) moieties in the hydrogel, the PG-responded PPNAH sensor could be facilely regenerated via a simple physical method at least fifty times while without compromising its response performance. Besides, our sensor was suitable for monitoring the PG-contaminated environmental water and displayed satisfactory detection performances. Such a sensor possessed obvious advantages of superior recyclability, highly chemical stability, low production cost, easy fabrication, wide range of visual detection, simple and intuitive operation for PG detection, and environmental-friendliness, which holds great potential in sensitive and colorimetric detection of the PG residues in polluted water.

One-step immunoassay based on filtration for detection of food poisoning-related bacteria

A one-step immunoassay based on filtration was presented, which used microbeads for target analyte detection and filters with appropriate pore sizes to distinguish the complexity of target analyte and microbeads. For effective bacterial detection, the microbead size and the filter's pore size must be optimized. The optimal concentrations of the enzyme (urease) and antibody were determined at the maximum absorbance change, that is, the maximum pH change. The pH change was measured using a field-effect transistor (FET). The correlation between pH change and threshold voltage was estimated to be 21.7 mV/pH, and the correlation between pH change and the source-drain current was estimated to be -379 nA/pH. For the one-step immunoassay, antibodies against target bacteria were isolated from horse serum by filtration, and these antibodies were estimated to have a sufficiently high specificity to overcome cross-reactivity among five types of food poisoning-related bacteria: Escherichia coli O157, Salmonella typhimurium, Listeria monocytogenes, Bacillus cereus, and Staphylococcus aureus. Finally, the FET-based one-step immunoassay was demonstrated for five types of food poisoning-related bacteria in human serum.

Laser desorption/ionization mass spectrometry of L-thyroxine (T4) using combi-matrix of α-cyano-4-hydroxycinnamic acid (CHCA) and graphene

An optimal combi-matrix for MALDI-TOF mass spectrometry was presented for the analysis of L-thyroxine (T4) in human serum. For the selection of the optimal combi-matrix, several kinds of combi-matrices were prepared by mixing the conventional organic matrix of CHCA with nanomaterials, such as graphene, carbon nanotubes, nanoparticles of Pt and TiO2. In order to select the optimal combi-matrix, the absorption at the wavelength of laser radiation (337 nm) for the ionization of sample was estimated using UV–Vis spectrometry. And, the heat absorption properties of these combi-matrices were also analyzed using differential scanning calorimetry (DSC), such as onset temperature and fusion enthalpy. In the case of the combi-matrix of CHCA and graphene, the onset temperature and fusion enthalpy were observed to be lower than those of CHCA, which represented the enhanced transfer of heat to the analyte in comparison with CHCA. From the analysis of optical and thermal properties, the combi-matrix of CHCA and graphene was selected to be an optimal combination for the transfer of laser energy during MALDI-TOF mass spectrometry. The feasibility of the combi-matrix composed of CHCA and graphene was demonstrated for the analysis of T4 molecules using MALDI-TOF mass spectrometry. The combi-matrix of CHCA and graphene was estimated to have an improved limit of detection and a wider detection range in comparison with other kinds of combi-matrices. Finally, the MALDI-TOF MS results of T4 analysis using combi-matrix were statistically compared with those of the conventional immunoassay.

Quantitative analysis of vitamin D using m/MALDI-TOF mass spectrometry based on a parylene matrix chip

Vitamin D deficiency is associated with various disorders and is diagnosed based on the concentration of 25-hydroxy vitamin D3 (25(OH)D3) in serum. The parylene matrix chip was fabricated to reduce the matrix background noise, and the homogenous distribution of the matrix was retained for the quantitative analysis of 25(OH)D3. The Amplex Red assay was performed to confirm that the sample-matrix mixing zone of the parylene matrix chip was formed below the surface of the parylene-N film. The homogeneous distribution of the matrix was verified from the fluorescence image. For effective analysis using a parylene matrix chip, 25(OH)D3 was modified through the nucleophilic addition of betaine aldehyde (BA) to form a hemiacetal salt. Such modified 25(OH)D3 with a positive charge from BA could be effectively analyzed using MALDI-TOF mass spectrometry. Serum 25(OH)D3 was extracted by liquid–liquid extraction (LLE) and quantified using MALDI-TOF mass spectrometry based on the parylene matrix chip. The intensity of the mass peak of 25(OH)D3 was linearly correlated (r2 = 0.992) with the concentration of 25(OH)D3 spiked in serum, and the LOD was 0.0056 pmol/μL. Energy drinks and vitamin D3 tablets were also employed for the real sample analysis. Finally, the results of the chemiluminescence binding assay and MALDI-TOF mass spectrometry were statistically analyzed to determine the applicability of the method using the Bland–Altman test and Passing–Bablok regression.

Eliminating sweet spot in MALDI-MS with hydrophobic ordered structure as target for quantifying biomolecules

In matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS), the analyte is usually distributed unevenly throughout the sample spot. The area with aggregated analyte molecules contributing abundant signal, is termed as "sweet spot", which results in poor detection reproducibility and makes it impossible to quantify analytes without internal standards. We proposed a strategy to eliminate sweet spot in MALDI-MS by using a hydrophobic ordered structure as target. The target is fabricated by creating a hydrophobic silicon nanopillar array and subsequently decorating it uniformly with poly(methyl methacrylate) nanodots for capturing analytes. The sweet spot is eliminated by distributing analyte molecules uniformly on this target, and then result in a uniform MS image, which demonstrates an ideal reproducibility. Finally, with the target assisted MALDI-MS as biosensor was suitable to analyze practical sample such as bacitracin A in milk. Horse heart myoglobin and, angiotensin III molecules can be quantified without internal standard using α-cyano-4-hydroxycinnamic acid as matrix. This biosensor presented good linearity, high salts tolerance and high signal-to-noise ratio (up to 271.8), even the 1 mol/L salt concentration. This strategy could provide an alternative for improving the performance of MALDI-MS.

Simultaneous Analysis of Multiple Cancer Biomarkers Using MALDI-TOF Mass Spectrometry Based on a Parylene-Matrix Chip

Recently, the parylene-matrix chip was developed for quantitative analysis of small molecules less than 1 kDa. In this study, MALDI-TOF MS based on the parylene-matrix chip was performed to clinically diagnose intrahepatic cholangiocarcinoma (IHCC) and colorectal cancer (CRC). The parylene-matrix chip was applied for the detection of small cancer biomarkers, including N-methyl-2-pyridone-5-carboxamide (2PY), glutamine, lysophosphatidylcholine (LPC) 16:0, and LPC 18:0. The feasibility of MALDI-TOF MS based on the parylene-matrix chip was confirmed via analysis of spot-to-spot and shot-to-shot reproducibility. Serum metabolite markers of IHCC, N-methyl-2-pyridone-5-carboxamide (2PY), and glutamine were quantified using MALDI-TOF MS based on the parylene-matrix chip. For clinical diagnosis of CRC, two water-insoluble (barely soluble) biomarkers, lysophosphatidylcholine (LPC) 16:0 and LPC 18:0, were quantified. Finally, glutamine and LPC 16:0 were simultaneously detected at a range of concentrations in sera from colon cancer patients using the parylene-matrix chip. Thus, this method yielded high-throughput detection of cancer biomarkers for the mixture samples of water-soluble analytes (2PY and glutamine) and water-insoluble analytes (LPC 16:0 and LPC 18:0).

TiO2 Nanowires from Wet-Corrosion Synthesis for Peptide Sequencing Using Laser Desorption/Ionization Time-of-Flight Mass Spectrometry

In this work, TiO₂ nanowires synthesized from a wet-corrosion process were presented for peptide sequencing by photocatalytic reaction with UV radiation. For the photocatalytic decomposition of peptides, the peptide sample was dropped on a target plate containing synthesized TiO₂ nanowire zones and UV-irradiated. Subsequently, the target plate was analyzed by laser desorption/ionization time-of-flight (LDI-TOF) mass spectrometry using the synthesized TiO₂ nanowires as a solid matrix. The feasibility of peptide sequencing based on the photocatalytic reaction with the synthesized TiO₂ nanowires was demonstrated using six types of peptides GHP9 (G₁-H-P-Q-G₂-K₁-K₂-K₃-K₄, 1006.59 Da), BPA-1(K₁-S₁-L-E-N-S₂-Y-G₁-G₂-G₃-K₂-K₃-K₄, 1394.74 Da), PreS1(F₁-G-A-N₁-S-N₂-N₃-P₁-D₁-W-D₂-F₂-N₄-P₂-N₅, 1707.68 Da), HPQ peptide-1 (G-Y-H-P-Q-R-K, 884.45 Da), HPQ peptide-2 (K-R-H-P-Q-Y-G, 884.45 Da), and HPQ peptide-3 (R-Y-H-P-Q-G-K, 884.45 Da). The identification of three different peptides with the same molecular weight was also demonstrated by using the synthesized TiO₂ nanowires for their photocatalytic decomposition as well as for LDI-TOF mass spectrometry as a solid-matrix.