Food packaging plays a vital role in protecting food products from environmental damage and preventing contamination from microorganisms. Conventional food packaging made of plastics produced from unrenewable fossil resources is hard to degrade and poses a negative impact on environmental sustainability. Natural biopolymers are attracting interest for reducing environmental problems to achieve a sustainable society, because of their abundance, biocompatibility, biodegradability, chemical stability, and non-toxicity. Active packaging systems composed of these biopolymers and biopolymer-based composites go beyond simply acting as a barrier to maintain food quality. This review provides a comprehensive overview of natural biopolymer materials used as matrices for food packaging. The antioxidant, water barrier, and oxygen barrier properties of these composites are compared and discussed. Furthermore, biopolymer-based composites integrated with antimicrobial agents—such as inorganic nanostructures and natural products—are reviewed, and the related mechanisms are discussed in terms of antimicrobial function. In summary, composites used for active food packaging systems can inhibit microbial growth and maintain food quality.

Fluorescence polarization (FP) has been applied in detecting chemicals and biomolecules for early-stage diagnosis, food safety analyses, and environmental monitoring. Compared to organic dyes, inorganic nanomaterials such as quantum dots have special fluorescence properties that can enhance the photostability of FP-based biosensing. In addition, nanomaterials, such as metallic nanoparticles, can be used as signal amplifiers to increase fluorescence polarization. In this review paper, different types of nanomaterials used in in FP-based biosensors have been reviewed. The role of each type of nanomaterial, acting as a fluorescent element and/or the signal amplifier, has been discussed. In addition, the advantages of FP-based biosensing systems have been discussed and compared with other fluorescence-based techniques. The integration of nanomaterials and FP techniques allows biosensors to quickly detect analytes in a sensitive and cost-effective manner and positively impact a variety of different fields including early-stage diagnoses.

Upconversion (UC) nanostructures, which can upconvert near-infrared (NIR) light with low energy to visible or UV light with higher energy, are investigated for theranostic applications. The surface of lanthanide (Ln)-doped UC nanostructures can be modified with different functional groups and bioconjugated with biomolecules for therapeutic systems. On the other hand, organic molecular-based UC nanostructures, by using the triplet-triplet annihilation (TTA) UC mechanism, have high UC quantum yields and do not require high excitation power. In this review, the major UC mechanisms in different nanostructures have been introduced, including the Ln-doped UC mechanism and the TTA UC mechanism. The design and fabrication of Ln-doped UC nanostructures and TTA UC-based UC nanostructures for theranostic applications have been reviewed and discussed. In addition, the current progress in the application of UC nanostructures for diagnosis and therapy has been summarized, including tumor-targeted bioimaging and chemotherapy, image-guided diagnosis and phototherapy, NIR-triggered controlled drug releasing and bioimaging. We also provide insight into the development of emerging UC nanostructures in the field of theranostics.

Quick separation of gram-negative bacteria, such as Escherichia coli (E. coli), from water sources is crucial for ensuring timely public health protection and promoting environmental sustainability. This study demonstrates that aptamer-conjugated core–shell magnetic nanoparticles (MNPs) can quickly capture E. coli DH5α from water. The core–shell MNP composed of an iron (Fe₃O₄) core and a silica (SiO₂) shell has been bio-conjugated with aptamers using glutaraldehyde as a cross-linker. The Fe₃O₄ core has an average diameter of approximately 16 ± 5 nm, and the thickness of the silica shell is around 24 ± 4 nm. Our results show that 1 mg mL⁻¹ of the Aptamer-Fe₃O₄@SiO₂ nanoparticles (NPs) can efficiently capture and remove E. coli DH5α cells (1 × 10⁷ CFU mL⁻¹) from aqueous solutions in just 5 minutes when subjected to an external magnetic field of 2.0 kOe. The selective interaction between E. coli DH5α and the Aptamer-Fe₃O₄@SiO₂ NPs has been analyzed as compared to the interaction between the Aptamer-Fe₃O₄@SiO₂ NPs and different strains of E. coli and gram-positive bacteria. This work demonstrates that the conjugation of aptamers on Fe₃O₄@SiO₂ NPs is a powerful tool for fast bacterial detection and magnetic isolation, supporting future use in monitoring water quality and protecting public health.