A9 bluff on flop but rivers some value

[RockRattler]

villain is 34/13/1.3 over few hands

I c/r on flop because his bet look very weak.
After his call I was in c/f mode.
On the river I try to get value fra a Q.

Party Poker, $0.50/$1 NL Hold'em Cash Game, 5 Players
LeggoPoker Hand History Converter

UTG: $103.35
CO: $120.89
BTN: $79.54
SB: $219.65
Hero (BB): $100

Pre-Flop: 9[img]/images/graemlins/heart.gif[/img] A[img]/images/graemlins/diamond.gif[/img] dealt to Hero (BB)
UTG folds, CO calls $1, 2 folds, Hero checks

Flop: ($2.50) 8[img]/images/graemlins/club.gif[/img] Q[img]/images/graemlins/diamond.gif[/img] 5[img]/images/graemlins/heart.gif[/img] (2 Players)
Hero checks, <font color="red">CO bets $1</font>, <font color="red">Hero raises to $5</font>, CO calls $4

Turn: ($12.50) 7[img]/images/graemlins/diamond.gif[/img] (2 Players)
Hero checks, CO checks

River: ($12.50) A[img]/images/graemlins/club.gif[/img] (2 Players)
<font color="red">Hero bets $7.50</font>, <font color="red">CO raises to $27</font>, Hero folds

When he raises I was confused but I guess A5 and A8 are very likely candidates for his hand.