Ratiometric fluorescence resonance energy transfer aptasensor for highly sensitive and selective detection of Acinetobacter baumannii bacteria in urine sample using carbon dots as optical nanoprobes

Development of sensitive and selective analytical method for accurate diagnosis of Acinetobacter baumannii (Ab) bacteria in biological samples is a challenge. Herein, we developed an ingenious ratiometric fluorescent aptasensor for sensitive and selective detection of (Ab) bacteria based on fluorescence resonance energy transfer (FRET) between ortho-phenylenediamines carbon dot (o-CD), nitrogen-doped carbon nanodots (NCND) as donor's species and graphene oxide (GO) as acceptor. NCND that assembled onto the edge of graphene oxide (GO) exhibited quenched photoluminescence emission, and with the absorption of the modified o-CD with aptamer (o-CD-ssDNA) onto the graphene oxide surface the fluorescence of o-CD was efficiently quenched. The aptamer (ssDNA) as a biorecognition element is bound with A. baumannii specifically which releases the o-CD-ssDNA from GO and the recovery of the fluorescence signal of o-CD, while the fluorescence intensity of NCND only slightly altered and acted as the reference signal in ratiometric fluorescence assay. The fluorescence intensity ratio (I 550 nm/I 440 nm) varied from 2.0 to 10.0 with the concentration of bacteria changing from 2.0 × 10 3 to 4.5 × 10 7 cfu/mL and the low detection limit of 3.0 × 10 2 cfu/mL (S/N = 3). The feasibility of the developed aptasensor for selective detection of A. baumannii in urine sample with satisfactory results was also demonstrated. An ingenious ratiometric fluorescent aptasensor developed for ultrasensitive and selective detection of Acinetobacter baumannii (Ab) bacteria based on fluorescence resonance energy transfer between ortho-phenylenediamines carbon dot (o-CD), as donor's, graphene oxide (GO) as acceptor and NCND as reference signal. • A ratiometric fluorescent aptasensor assay developed for detection of A. baumannii bacteria. • o-CD/nitrogen-doped-CD (NCND) and (GO) used as donor and acceptor, respectively in FRET process. • The assay applied for A. baumannii bacteria detection at concentration range 2.0 × 10 3 –4.5 × 10 7 cfu mL −1. • Proposed assay developed for bacteria detection in urine with satisfactory results and DL of 0.3 Kcfu.