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The determination of lactic acid content has a guiding significance for disease diagnosis or food supervision. Herein, a hydrogel-based three-dimensional photonic crystal (PC) sensor for specific detection of lactic acid is introduced. The hydrogel was prepared by one-step copolymerization of N-isopropylacrylamide and acrylamide in the presence of oxamate derivative 2-((6-acrylamidohexyl) amino)-2-oxoacetic acid (AOA). An obvious color change from orange-red to purple and a 45-nm redshift of the reflection peak were obtained in 3 min when lactic acid concentration increased from 0 to 20 mM. The detection limit was confirmed as 0.1 mM, and the prepared sensor can be reused more than 20 times. Moreover, the affinity and selectivity of AOA to lactic acid were proven by both the interaction energy from density functional theory (DFT) study and the comparison to those of pyruvate and propionic acid. This sensor was proven to be cost-effective and convenient with rapid response time, good reusability, and selectivity. [ABSTRACT FROM AUTHOR]

[Display omitted] • A pH-responsive discoloration photonic crystal sensor was proposed for amniotic fluid recognition. • The sensor showed the high accuracy and sensitivity, rapid response and visual detection. • Compared with pH test paper, a noticeable color difference and extraordinary accuracy were obtained. In this study, we proposed a pH-responsive photonic crystal hydrogel sensor (PCHs) to conveniently and accurately recognize the amniotic fluid from urine of parturient women, which was constituted by three-dimensional polymethyl acrylamide (PMMA) array and optimized hydrogel. PMMA array was self-assembled by 180 nm monodispersed nanoparticles with vertical sedimentation method. The functional hydrogel containing N-acryloyl phenylalanine (APA), acrylamide (AM) and N, N'-methylene bis(acrylamide) (BIS) as co-monomer and crosslinking agent respectively, was photo-polymerized by the precursor under 365 nm UV light. This hydrogel significantly shrank or swelled corresponding to the acidity and alkalinity of the aqueous solution, which resulted in both the reflection peak position (λ max) of the prepared sensor and its structural color changing with the pH value. The λ max of PCHs redshifted from 514 nm to 606 nm in 60 s while the pH value of testing solution increased from 4.5 to 8.0, which exactly covered the pH value of amniotic fluid and urine. Correspondingly, its structure color gradually changed from pale-green to red ensuring their naked-eye determination. Furthermore, an extremely high sensitivity as 26.3 nm/pH of Δ λ max was obtained which was linearly related to pH value. The prepared sensor possessed steady accuracy and extraordinary sensitivity compared with the pH test strip which was generally used in amniorrhexis diagnosis nowadays besides the advantages of the low cost, simple operation, rapid response and visual detection mode. The reliability of this PCHs was further confirmed by the real sample detection which relative standard deviation was below 5.0 %, suggesting its potential clinical applications. [ABSTRACT FROM AUTHOR]

The detection of the human immunodeficiency virus-1 (HIV) at an early stage is vital and could be realized through its cell surface glycoprotein-120 (gp120) without virus preprocessing. Here, we present an ssDNA-aptamer-linked photonic crystal (APC) hydrogel sensor for HIV detection which is comprised of photonic crystals (PCs) made of polystyrene nanoparticles embedded in the polyacrylamide hydrogel. ssDNA aptamers specific for gp120 are crosslinked in the hydrogel which can selectively bind to gp120 by hydrogen bonding increasing the PCs particle spacing and swelling of the hydrogel. The binding response can be visually monitored as a color change due to the diffraction of light from PCs and can eventually be measured (1–1000 ng mL−1 of gp120) and 100 to 108 VP mL−1 of HIV by the Debye's ring diameter or a UV/Vis spectrometer. APC-hydrogel can be regenerated by Tris-HCl and EDTA washing buffer system. The sensor demonstrates LOD of 7.1 ± 1.55 ng mL−1 for gp120 and 4 VP mL−1 for the whole HIV, a rapid response of 5 min, reusability up to 70 % (in fifth use), and recovery of 95.4 ± 0.1 % to 99.0 ± 0.2 % in plasma samples. The sensor is cost-effect and stable compared to antibody-based sensors and can be utilized to develop point-of-care testing (POCT) devices for HIV diagnosis. [Display omitted] • A novel ssDNA aptamer linked photonic crystal sensor for rapid, sensitive, and onsite quantitative detection of HIV. • Specific binding of the aptamer to gp120 results in reversible swelling of the hydrogel. • Photonic crystals embedded in the polyacrylamide hydrogel provide a vibrant optical response visible to the naked eye. [ABSTRACT FROM AUTHOR]